Using Lubuntu session on amd64, confirmed crash even when switching themes. Bt : 

Program received signal SIGSEGV, Segmentation fault.
__strcmp_ssse3 () at ../sysdeps/x86_64/multiarch/../strcmp.S:210
210	../sysdeps/x86_64/multiarch/../strcmp.S: Aucun fichier ou dossier de ce type.
(gdb) bt full
#0  __strcmp_ssse3 () at ../sysdeps/x86_64/multiarch/../strcmp.S:210
No locals.
#1  0x00007ffff0fcc188 in add_to_rc_file_list (rc_file_list=0x7fffe765f928, filename=0x500000090 <error: Cannot access memory at address 0x500000090>, 
    reload=0) at /build/buildd/gtk+2.0-2.24.22/gtk/gtkrc.c:960
        tmp_list = 0x7ffff6c80f30
        rc_file = 0x7fffe6cdfee0
#2  0x00007ffff0fd0e3c in gtk_rc_context_parse_one_file (context=context@entry=0x7fffe765f900, 
    filename=filename@entry=0x500000090 <error: Cannot access memory at address 0x500000090>, priority=priority@entry=12, reload=reload@entry=0)
    at /build/buildd/gtk+2.0-2.24.22/gtk/gtkrc.c:994
        rc_file = <optimized out>
        statbuf = {st_dev = 12, st_ino = 140737241730391, st_nlink = 0, st_mode = 1431724632, st_uid = 21845, st_gid = 4, __pad0 = 0, 
          st_rdev = 93824992304231, st_size = 4, st_blksize = 3, st_blocks = 2, st_atim = {tv_sec = 140737035542656, tv_nsec = 12}, st_mtim = {tv_sec = 2, 
            tv_nsec = 140737035542656}, st_ctim = {tv_sec = 93824992300561, tv_nsec = 335736625}, __unused = {140737352896584, 140737075607808, 0}}
        saved_priority = 12
        __FUNCTION__ = "gtk_rc_context_parse_one_file"
#3  0x00007ffff0fd10cf in gtk_rc_context_parse_file (context=context@entry=0x7fffe765f900, 
    filename=0x500000090 <error: Cannot access memory at address 0x500000090>, priority=priority@entry=12, reload=reload@entry=0)
    at /build/buildd/gtk+2.0-2.24.22/gtk/gtkrc.c:1099
        locale_suffixes = {0x7fffe94fe6b0 "fr_FR", 0x7fffe94fe6c0 "fr"}
        n_locale_suffixes = 2
        p = <optimized out>
        locale = <optimized out>
        length = <optimized out>
        j = <optimized out>
        found = 0
#4  0x00007ffff0fd193f in gtk_rc_parse_default_files (context=0x7fffe765f900) at /build/buildd/gtk+2.0-2.24.22/gtk/gtkrc.c:862
        i = <optimized out>
#5  IA__gtk_rc_reparse_all_for_settings (settings=settings@entry=0x7ffff6ceab40, force_load=force_load@entry=1)
    at /build/buildd/gtk+2.0-2.24.22/gtk/gtkrc.c:1809
        mtime_modified = <optimized out>
        rc_file = <optimized out>
        tmp_list = <optimized out>
        context = 0x7fffe765f900
        statbuf = {st_dev = 0, st_ino = 140737241743257, st_nlink = 140737244752912, st_mode = 1431723111, st_uid = 21845, st_gid = 4051364880, 
          __pad0 = 32767, st_rdev = 32, st_size = 0, st_blksize = 140737333981200, st_blocks = 140737107142832, st_atim = {tv_sec = 0, 
            tv_nsec = 140737107142832}, st_mtim = {tv_sec = 93824992305752, tv_nsec = 140737107142832}, st_ctim = {tv_sec = 32, tv_nsec = 140737334127424}, 
          __unused = {140737241830961, 621, 140737241698303}}
        __FUNCTION__ = "IA__gtk_rc_reparse_all_for_settings"
#6  0x00007ffff0fed842 in IA__gtk_settings_get_for_screen (screen=0x7ffff6cc7000) at /build/buildd/gtk+2.0-2.24.22/gtk/gtksettings.c:1265
        settings = 0x7ffff6ceab40
        __FUNCTION__ = "IA__gtk_settings_get_for_screen"
#7  0x00007ffff0fed89a in IA__gtk_settings_get_default () at /build/buildd/gtk+2.0-2.24.22/gtk/gtksettings.c:1293
        screen = <optimized out>
#8  0x00007ffff1002189 in gtk_style_init (style=0x7fffe501c030) at /build/buildd/gtk+2.0-2.24.22/gtk/gtkstyle.c:420
        i = <optimized out>
        settings = <optimized out>
#9  0x00007ffff17cae3b in g_type_create_instance (type=<optimized out>) at /build/buildd/glib2.0-2.39.90/./gobject/gtype.c:1868
        instance = 0x7fffe501c030
        class = 0x7fffe94728b0
        allocated = <optimized out>
        private_size = <optimized out>
        ivar_size = <optimized out>
---Type <return> to continue, or q <return> to quit---
        i = 0
#10 0x00007ffff17af355 in g_object_new_internal (class=class@entry=0x7fffe94728b0, params=params@entry=0x0, n_params=n_params@entry=0)
    at /build/buildd/glib2.0-2.39.90/./gobject/gobject.c:1724
        nqueue = 0x0
        object = <optimized out>
        __FUNCTION__ = "g_object_new_internal"
#11 0x00007ffff17b110d in g_object_newv (object_type=object_type@entry=140737106719136, n_parameters=n_parameters@entry=0, parameters=parameters@entry=0x0)
    at /build/buildd/glib2.0-2.39.90/./gobject/gobject.c:1868
        class = 0x7fffe94728b0
        unref_class = 0x7fffe94728b0
        object = <optimized out>
        __FUNCTION__ = "g_object_newv"
#12 0x00007ffff17b18bc in g_object_new (object_type=140737106719136, first_property_name=first_property_name@entry=0x0)
    at /build/buildd/glib2.0-2.39.90/./gobject/gobject.c:1568
        var_args = {{gp_offset = 4048687393, fp_offset = 32767, overflow_arg_area = 0x7fffe940d4b0, 
            reg_save_area = 0x7ffff17ae064 <g_object_notify_queue_thaw+388>}}
        __FUNCTION__ = "g_object_new"
#13 0x00007ffff1002619 in IA__gtk_style_new () at /build/buildd/gtk+2.0-2.24.22/gtk/gtkstyle.c:694
No locals.
#14 0x00007ffff1099909 in IA__gtk_widget_get_default_style () at /build/buildd/gtk+2.0-2.24.22/gtk/gtkwidget.c:7244
No locals.
#15 0x00007ffff10999b8 in gtk_widget_init (widget=0x7fffe940f420) at /build/buildd/gtk+2.0-2.24.22/gtk/gtkwidget.c:2892
No locals.
#16 0x00007ffff17cadf8 in g_type_create_instance (type=<optimized out>) at /build/buildd/glib2.0-2.39.90/./gobject/gtype.c:1862
        instance = 0x7fffe940f420
        class = 0x7fffe5013c00
        allocated = <optimized out>
        private_size = <optimized out>
        ivar_size = <optimized out>
        i = 1
#17 0x00007ffff17aef38 in g_object_constructor (type=<optimized out>, n_construct_properties=0, construct_params=0x0)
    at /build/buildd/glib2.0-2.39.90/./gobject/gobject.c:2006
        object = <optimized out>
#18 0x00007ffff0f7587b in gtk_invisible_constructor (type=<optimized out>, n_construct_properties=<optimized out>, construct_params=<optimized out>)
    at /build/buildd/gtk+2.0-2.24.22/gtk/gtkinvisible.c:315
        object = <optimized out>
#19 0x00007ffff17af9de in g_object_new_with_custom_constructor (n_params=0, params=0x0, class=0x7fffe5013c00)
    at /build/buildd/glib2.0-2.39.90/./gobject/gobject.c:1645
        cparams = 0x0
        cvalues = 0x0
        node = 0x0
        i = 0
        nqueue = 0x0
        object = <optimized out>
        n_cparams = 0
        cvals_used = 0
#20 g_object_new_internal (class=class@entry=0x7fffe5013c00, params=params@entry=0x0, n_params=n_params@entry=0)
    at /build/buildd/glib2.0-2.39.90/./gobject/gobject.c:1722
        nqueue = 0x0
        object = <optimized out>
        __FUNCTION__ = "g_object_new_internal"
#21 0x00007ffff17b110d in g_object_newv (object_type=object_type@entry=140737106800128, n_parameters=n_parameters@entry=0, parameters=parameters@entry=0x0)
---Type <return> to continue, or q <return> to quit---
    at /build/buildd/glib2.0-2.39.90/./gobject/gobject.c:1868
        class = 0x7fffe5013c00
        unref_class = 0x7fffe5013c00
        object = <optimized out>
        __FUNCTION__ = "g_object_newv"
#22 0x00007ffff17b18bc in g_object_new (object_type=140737106800128, first_property_name=0x0) at /build/buildd/glib2.0-2.39.90/./gobject/gobject.c:1568
        var_args = {{gp_offset = 4294952416, fp_offset = 32767, overflow_arg_area = 0x7fffe941ee00, 
            reg_save_area = 0x7ffff1521299 <g_rw_lock_writer_unlock+9>}}
        __FUNCTION__ = "g_object_new"
#23 0x00007ffff326c97a in nsLookAndFeel::Init (this=0x7ffff6c5fd20) at /build/buildd/firefox-28.0~b2+build1/widget/gtk/nsLookAndFeel.cpp:916
        parent = <optimized out>
        style = <optimized out>
        linkButton = <optimized out>
        colorValuePtr = 0x7fffffffcb60
        menuitem = <optimized out>
        treeView = <optimized out>
        menuBar = <optimized out>
        entry = <optimized out>
        param_spec = <optimized out>
        widget = <optimized out>
        accel_label = <optimized out>
        button = <optimized out>
        comboboxLabel = <optimized out>
        supports_menubar_drag = -14536
        value = 32767
        colorValue = {pixel = 0, red = 51648, green = 63170, blue = 32767}
        menu = <optimized out>
        label = <optimized out>
        combobox = <optimized out>
        window = <optimized out>
#24 0x00007ffff328bea3 in nsXPLookAndFeel::GetInstance () at /build/buildd/firefox-28.0~b2+build1/widget/xpwidgets/nsXPLookAndFeel.cpp:252
No locals.
#25 0x00007ffff328c60b in mozilla::LookAndFeel::GetInt (aID=mozilla::LookAndFeel::eIntID_UseAccessibilityTheme, aResult=0x7fffffffc738)
    at /build/buildd/firefox-28.0~b2+build1/widget/xpwidgets/nsXPLookAndFeel.cpp:718
No locals.
#26 0x00007ffff2be7177 in GetInt (aDefault=0, aID=mozilla::LookAndFeel::eIntID_UseAccessibilityTheme) at ../../dist/include/mozilla/LookAndFeel.h:519
        result = -222671937
#27 nsChromeRegistryChrome::CheckForOSAccessibility (this=0x7ffff6c176e0) at /build/buildd/firefox-28.0~b2+build1/chrome/src/nsChromeRegistryChrome.cpp:168
No locals.
#28 0x00007ffff3ab9a73 in ScopedXPCOMStartup::SetWindowCreator (this=<optimized out>, native=<optimized out>)
    at /build/buildd/firefox-28.0~b2+build1/toolkit/xre/nsAppRunner.cpp:1284
        rv = NS_OK
        cr = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c176e0}, <No data fields>}
        creator = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff2bdb7be <mozilla::BackgroundHangManager::MonitorThread(void*)>}, <No data fields>}
        wwatch = {<nsCOMPtr_base> = {mRawPtr = 0x7fffe508c830}, <No data fields>}
#29 0x00007ffff3abd5f4 in XREMain::XRE_mainRun (this=this@entry=0x7fffffffc960) at /build/buildd/firefox-28.0~b2+build1/toolkit/xre/nsAppRunner.cpp:3841
        rv = NS_OK
        appStartup = {<nsCOMPtr_base> = {mRawPtr = 0x7fffffffc878}, <No data fields>}
        workingDir = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff7ed1048}, <No data fields>}
        prefs = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c7ca80}, <No data fields>}
        userAgentLocale = {<nsACString_internal> = {mData = 0x7fff00000000 <error: Cannot access memory at address 0x7fff00000000>, mLength = 4139963840, 
            mFlags = 32767}, <No data fields>}
---Type <return> to continue, or q <return> to quit---
        cmdLine = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2c6c0}, <No data fields>}
#30 0x00007ffff3abe225 in XREMain::XRE_main (this=this@entry=0x7fffffffc960, argc=argc@entry=1, argv=argv@entry=0x7fffffffde58, 
    aAppData=aAppData@entry=0x7fffffffcb60) at /build/buildd/firefox-28.0~b2+build1/toolkit/xre/nsAppRunner.cpp:4127
        aLocal = 0 '\000'
        sampler_raii4077 = {mHandle = 0x7ffff6ca5000}
        rv = <optimized out>
        exit = false
        appInitiatedRestart = false
        result = <optimized out>
#31 0x00007ffff3abe48a in XRE_main (argc=1, argv=0x7fffffffde58, aAppData=0x7fffffffcb60, aFlags=<optimized out>)
    at /build/buildd/firefox-28.0~b2+build1/toolkit/xre/nsAppRunner.cpp:4337
        main = {mNativeApp = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6cfc880}, <No data fields>}, mProfileSvc = {<nsCOMPtr_base> = {
              mRawPtr = 0x7fffe941c880}, <No data fields>}, mProfD = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2d380}, <No data fields>}, 
          mProfLD = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2d440}, <No data fields>}, mProfileLock = {<nsCOMPtr_base> = {
              mRawPtr = 0x7fffe94189a0}, <No data fields>}, mRemoteService = {<nsCOMPtr_base> = {mRawPtr = 0x0}, <No data fields>}, 
          mScopedXPCom = 0x7ffff6c7ca80, mAppData = 0x7ffff6c24880, mDirProvider = 
    {<nsIDirectoryServiceProvider2> = {<nsIDirectoryServiceProvider> = {<nsISupports> = {
                  _vptr.nsISupports = 0x7ffff52d2530 <vtable for nsXREDirProvider+16>}, <No data fields>}, <No data fields>}, <nsIProfileStartup> = {<nsISupports> = {_vptr.nsISupports = 0x7ffff52d2578 <vtable for nsXREDirProvider+88>}, <No data fields>}, mAppProvider = {<nsCOMPtr_base> = {
                mRawPtr = 0x0}, <No data fields>}, mGREDir = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2c6c0}, <No data fields>}, 
            mXULAppDir = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2c9c0}, <No data fields>}, mProfileDir = {<nsCOMPtr_base> = {
                mRawPtr = 0x7ffff6c2d380}, <No data fields>}, mProfileLocalDir = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2d440}, <No data fields>}, 
            mProfileNotified = false, mAppBundleDirectories = {<nsCOMArray_base> = {
                mArray = {<nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator>> = {<nsTArray_base<nsTArrayInfallibleAllocator, nsTArray_CopyWithMemutils>> = {
                      mHdr = 0x7ffff5430b40 <nsTArrayHeader::sEmptyHdr>}, <nsTArray_TypedBase<nsISupports*, nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator> >> = {<nsTArray_SafeElementAtHelper<nsISupports*, nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator> >> = {<No data fields>}, <No data fields>}, <No data fields>}, <No data fields>}}, <No data fields>}, mExtensionDirectories = {<nsCOMArray_base> = {
                mArray = {<nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator>> = {<nsTArray_base<nsTArrayInfallibleAllocator, nsTArray_CopyWithMemutils>> = {
                      mHdr = 0x7ffff5430b40 <nsTArrayHeader::sEmptyHdr>}, <nsTArray_TypedBase<nsISupports*, nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator> >> = {<nsTArray_SafeElementAtHelper<nsISupports*, nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator> >> = {<No data fields>}, <No data fields>}, <No data fields>}, <No data fields>}}, <No data fields>}, mThemeDirectories = {<nsCOMArray_base> = {
                mArray = {<nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator>> = {<nsTArray_base<nsTArrayInfallibleAllocator, nsTArray_CopyWithMemutils>> = {
                      mHdr = 0x7ffff5430b40 <nsTArrayHeader::sEmptyHdr>}, <nsTArray_TypedBase<nsISupports*, nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator> >> = {<nsTArray_SafeElementAtHelper<nsISupports*, nsTArray_Impl<nsISupports*, nsTArrayInfallibleAllocator> >> = {<No data fields>}, <No data fields>}, <No data fields>}, <No data fields>}}, <No data fields>}}, mProfileName = {<nsFixedCString> = {<nsCString> = {<nsACString_internal> = {mData = 0x7ffff6cfcab8 "default", 
                  mLength = 7, mFlags = 65541}, <No data fields>}, mFixedCapacity = 63, mFixedBuf = 0x7fffffffca18 ""}, 
            mStorage = "\000\312\377\377\377\177\000\000\237\312\377\377\377\177\000\000\230\312\377\377\377\177\000\000\237\312\377\377\377\177\000\000\237\312\377\377\377\177\000\000\060\313\377\377\377\177\000\000x\312\377\377\377\177\000\000\300\311\302\366\377\177\000"}, 
          mDesktopStartupID = {<nsFixedCString> = {<nsCString> = {<nsACString_internal> = {mData = 0x7fffffffca78 "", mLength = 0, 
                  mFlags = 65553}, <No data fields>}, mFixedCapacity = 63, mFixedBuf = 0x7fffffffca78 ""}, 
            mStorage = "\000\312\377\377\377\177\000\000\a\000\000\000\021\000\001\000?\000\000\000\377\177\000\000\230\312\377\377\377\177\000\000browser\000\300\306\302\366\377\177\000\000\250\311\302\366\377\177\000\000H\313\377\377\377\177\000"}, mStartOffline = false, mShuttingDown = false, 
          mDisableRemote = false, mGdkDisplay = 0x7ffff6cdf020}
        result = <optimized out>
#32 0x00005555555583c1 in do_main (argc=1, argv=0x7fffffffde58, xreDirectory=0x7ffff6c2c6c0)
    at /build/buildd/firefox-28.0~b2+build1/browser/app/nsBrowserApp.cpp:280
        appData = {<nsXREAppData> = {size = 120, directory = 0x7ffff6c2c9c0, vendor = 0x7ffff6c7c2c8 "Mozilla", name = 0x7ffff6c7c2d0 "Firefox", 
            version = 0x7ffff6c7c2d8 "28.0", buildID = 0x7ffff6c23690 "20140226081007", ID = 0x7ffff6c8e610 "{ec8030f7-c20a-464f-9b0e-13a3a9e97384}", 
            copyright = 0x0, flags = 14, xreDirectory = 0x7ffff6c2c6c0, minVersion = 0x7ffff6c7c2e0 "28.0", maxVersion = 0x7ffff6c7c2e8 "28.0", 
---Type <return> to continue, or q <return> to quit---
            crashReporterURL = 0x7ffff6c24600 "https://crash-reports.mozilla.com/submit?id={ec8030f7-c20a-464f-9b0e-13a3a9e97384}&version=28.0&buildid=20140226081007", profile = 0x0, UAName = 0x0}, <No data fields>}
        exeFile = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2c840}, <No data fields>}
        greDir = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2c900}, <No data fields>}
        appSubdir = {<nsCOMPtr_base> = {mRawPtr = 0x7ffff6c2c9c0}, <No data fields>}
        rv = <optimized out>
        appDataFile = <optimized out>
        metroOnDesktop = false
        appini = {<nsCOMPtr_base> = {mRawPtr = 0x0}, <No data fields>}
#33 0x0000555555557b7c in main (argc=1, argv=0x7fffffffde58) at /build/buildd/firefox-28.0~b2+build1/browser/app/nsBrowserApp.cpp:648
        gotCounters = 1
        initialRUsage = {ru_utime = {tv_sec = 0, tv_usec = 2692}, ru_stime = {tv_sec = 0, tv_usec = 2021}, {ru_maxrss = 15100, __ru_maxrss_word = 15100}, {
            ru_ixrss = 0, __ru_ixrss_word = 0}, {ru_idrss = 0, __ru_idrss_word = 0}, {ru_isrss = 0, __ru_isrss_word = 0}, {ru_minflt = 684, 
            __ru_minflt_word = 684}, {ru_majflt = 0, __ru_majflt_word = 0}, {ru_nswap = 0, __ru_nswap_word = 0}, {ru_inblock = 0, __ru_inblock_word = 0}, {
            ru_oublock = 0, __ru_oublock_word = 0}, {ru_msgsnd = 0, __ru_msgsnd_word = 0}, {ru_msgrcv = 0, __ru_msgrcv_word = 0}, {ru_nsignals = 0, 
            __ru_nsignals_word = 0}, {ru_nvcsw = 6, __ru_nvcsw_word = 6}, {ru_nivcsw = 3, __ru_nivcsw_word = 3}}
        xreDirectory = 0x7ffff6c2c6c0
        rv = <optimized out>
        result = <optimized out>
(gdb)