ubuntu bug: https://bugs.edge.launchpad.net/bugs/401055

Stacktrace with --sync on ffox 3.5.1: http://launchpadlibrarian.net/29324303/StackTraceDebug.txt
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#2  0x00007fda15006256 in ?? () from /usr/lib/libgdk-x11-2.0.so.0
No symbol table info available.
#3  0x00007fda16f503d4 in _XError (dpy=0x7fda1a6ac000, rep=0x7fda1a6b8100) at ../../src/XlibInt.c:2924
        rtn_val = <value optimized out>
        event = {type = 0, xany = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819}, xkey = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819, root = 4256530, subwindow = 550, time = 140574722708608, x = 549, y = 0, x_root = 443203584, y_root = 32730, state = 443252992, keycode = 32730, same_screen = 1}, xbutton = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819, root = 4256530, subwindow = 550, time = 140574722708608, x = 549, y = 0, x_root = 443203584, y_root = 32730, state = 443252992, button = 32730, same_screen = 1}, xmotion = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819, root = 4256530, subwindow = 550, time = 140574722708608, x = 549, y = 0, x_root = 443203584, y_root = 32730, state = 443252992, is_hint = -38 '\332', same_screen = 1}, xcrossing = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819, root = 4256530, subwindow = 550, time = 140574722708608, x = 549, y = 0, x_root = 443203584, y_root = 32730, mode = 443252992, detail = 32730, same_screen = 1, focus = 0, state = 550}, xfocus = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819, mode = 4256530, detail = 0}, xexpose = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819, x = 4256530, y = 0, width = 550, height = 0, count = 443110528}, xgraphicsexpose = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, drawable = 140574715810819, x = 4256530, y = 0, width = 550, height = 0, count = 443110528, major_code = 32730, minor_code = 549}, xnoexpose = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, drawable = 140574715810819, major_code = 4256530, minor_code = 0}, xvisibility = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819, state = 4256530}, xcreatewindow = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, parent = 140574715810819, window = 4256530, x = 550, y = 0, width = 443110528, height = 32730, border_width = 549, override_redirect = 0}, xdestroywindow = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, event = 140574715810819, window = 4256530}, xunmap = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, event = 140574715810819, window = 4256530, from_configure = 550}, xmap = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, event = 140574715810819, window = 4256530, override_redirect = 550}, xmaprequest = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, parent = 140574715810819, window = 4256530}, xreparent = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, event = 140574715810819, window = 4256530, parent = 550, x = 443110528, y = 32730, override_redirect = 549}, xconfigure = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, event = 140574715810819, window = 4256530, x = 550, y = 0, width = 443110528, height = 32730, border_width = 549, above = 140574722801664, override_redirect = 443252992}, xgravity = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, event = 140574715810819, window = 4256530, x = 550, y = 0}, xresizerequest = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, window = 140574715810819, width = 4256530, height = 0}, xconfigurerequest = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, parent = 140574715810819, window = 4256530, x = 550, y = 0, width = 443110528, height = 32730, border_width = 549, above = 140574722801664, detail = 443252992, value_mask = 1}, xcirculate = {type = 0, serial = 140574722801664, send_event = 83886083, display = 0x226, event = 140574715810819, window = 4256530, place = 550}, xci
        async = <value optimized out>
        next = 0x7fda1a6b8100
#4  0x00007fda16f56e76 in _XReply (dpy=0x7fda1a6ac000, rep=<value optimized out>, extra=0, discard=0) at ../../src/xcb_io.c:506
        ext = 0x0
        ret_code = <value optimized out>
        error = 0x7fda1a6b8100
        c = 0x7fda1a6ad000
        __PRETTY_FUNCTION__ = "_XReply"
#5  0x00007fda16f343e7 in XGetWindowProperty (dpy=0x7fda1a6ac000, w=<value optimized out>, property=327, offset=0, length=0, delete=1870209126, req_type=0, actual_type=0x7fffa6752e70, actual_format=0x7fffa6752e7c, nitems=0x7fffa6752e68, bytesafter=0x7fffa6752e60, prop=0x7fffa6752e58) at ../../src/GetProp.c:64
        reply = {type = 0 '\0', format = 3 '\3', sequenceNumber = 550, length = 83886083, propertyType = 1310720, bytesAfter = 0, nItems = 78567008, pad1 = 0, pad2 = 3, pad3 = 0}
        error = {type = 0 '\0', errorCode = 192 '\300', sequenceNumber = 550, resourceID = 32730, minorCode = 28514, majorCode = 245 '\365', pad1 = 22 '\26', pad3 = 32730, pad4 = 443171200, pad5 = 32730, pad6 = 443207680, pad7 = 32730}
#6  0x00007fda18c36450 in XRemoteClient::CheckWindow (this=0x7fffa6753050, aWindow=0) at XRemoteClient.cpp:273
        type = 0
        nitems = 140735986085968
        data = <value optimized out>
        format = 32767
        bytesafter = 0
        innerWindow = <value optimized out>
#7  0x00007fda18c36578 in XRemoteClient::FindBestWindow (this=0x7fffa6753050, aProgram=<value optimized out>, aUsername=<value optimized out>, aProfile=<value optimized out>, aSupportsCommandLine=<value optimized out>) at XRemoteClient.cpp:489
        type = 0
        nitems = 0
        data_return = 0x0
        w = 0
        status = 464016024
        username = 0x1 <Address 0x1 out of bounds>
        format = 0
        bytesafter = 0
        version = 0
        bestWindow = 77594697
        parent = 0
        nkids = 154
        i = <value optimized out>
        root2 = 292
        kids = 0x7fda1a69f800
#8  0x00007fda18c36b98 in XRemoteClient::SendCommandLine (this=0x1, aProgram=0x0, aUsername=0x7fda1ba85298 "\235\216\377\377Ȏ\377\377\210\216\377\377\235\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377\350\216\377\377\200\217\377\377\350\216\377\377\350\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377Џ\377\377\30\220\377\377Џ\377\377Џ\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377m\216\377\377Џ\377\377\350\220\377\377"..., aProfile=0xc <Address 0xc out of bounds>, argc=2, argv=0x726220756f792066, aDesktopStartupID=0x0, aResponse=0x7fffa6753348, aWindowFound=0x7fffa67534b0) at XRemoteClient.cpp:228
        w = <value optimized out>
        rv = 0
...