also happens without the epiphany extensions:

jos@hamerkeuh:~$ epiphany

** (epiphany-browser:16489): WARNING **: Could not determine locale 111!

LoadPlugin: failed to initialize shared library /usr/lib/totem/gstreamer/libtotem-complex-plugin.so [/usr/lib/totem/gstreamer/libtotem-complex-plugin.so: undefined symbol: _ZN13nsTArray_base9sEmptyHdrE]
*** glibc detected *** epiphany-browser: double free or corruption (!prev): 0x08b7d7b8 ***
======= Backtrace: =========
/lib/tls/i686/cmov/libc.so.6[0xb6ece975]
/lib/tls/i686/cmov/libc.so.6(cfree+0x90)[0xb6ed23e0]
/usr/lib/xulrunner-1.9b3pre/libmozjs.so[0xb5cdf665]
/usr/lib/xulrunner-1.9b3pre/libmozjs.so[0xb5c9a471]
/usr/lib/xulrunner-1.9b3pre/libmozjs.so(JS_GC+0x3a)[0xb5c711ea]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb4fb60b5]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb59adc80]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb59adcfe]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb54693a9]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb5469687]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb59a3450]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb59a3528]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb59a0467]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb5961e87]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb58af046]
/usr/lib/xulrunner-1.9b3pre/libxul.so[0xb589afcc]
/usr/lib/libglib-2.0.so.0[0xb714337d]
/usr/lib/libglib-2.0.so.0(g_main_context_dispatch+0x176)[0xb710ed96]
/usr/lib/libglib-2.0.so.0[0xb7112153]
/usr/lib/libglib-2.0.so.0(g_main_loop_run+0x1e7)[0xb7112537]
/usr/lib/libgtk-x11-2.0.so.0(gtk_main+0xb4)[0xb78588d4]
epiphany-browser(main+0x74d)[0x807628d]
/lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe0)[0xb6e79450]
epiphany-browser[0x8075851]
======= Memory map: ========
08048000-08158000 r-xp 00000000 08:02 114317     /usr/bin/epiphany-gecko
08158000-08163000 rwxp 0010f000 08:02 114317     /usr/bin/epiphany-gecko
08163000-0906d000 rwxp 08163000 00:00 0          [heap]
afc82000-afc8a000 rwxp afc82000 00:00 0 
afc8a000-afcbd000 r-xp 00000000 08:02 979284     /usr/share/fonts/truetype/msttcorefonts/Arial_Italic.ttf
afcbd000-afcbe000 ---p afcbd000 00:00 0 
afcbe000-b04be000 rwxp afcbe000 00:00 0 
b04be000-b054e000 r-xp 00000000 08:02 310190     /usr/share/fonts/truetype/ttf-dejavu/DejaVuSans.ttf
b054e000-b0570000 r-xp 00000000 08:02 979271     /usr/share/fonts/truetype/msttcorefonts/Verdana_Bold.ttf
b0570000-b0593000 r-xp 00000000 08:02 979294     /usr/share/fonts/truetype/msttcorefonts/Georgia.ttf
b0593000-b059b000 r-xp 00000000 08:02 492299     /usr/share/locale-langpack/en_GB/LC_MESSAGES/totem.mo
b059b000-b05ba000 r-xp 00000000 08:02 979298     /usr/share/fonts/truetype/msttcorefonts/Trebuchet_MS_Bold.ttf
b05ba000-b0600000 r-xp 00000000 08:02 979285     /usr/share/fonts/truetype/msttcorefonts/Arial_Bold.ttf
b0600000-b0646000 rwxp b0600000 00:00 0 
b0646000-b0700000 ---p b0646000 00:00 0 
b070d000-b0751000 r-xp 00000000 08:02 979287     /usr/share/fonts/truetype/msttcorefonts/Arial.ttf
b0751000-b0755000 r-xp 00000000 08:02 410625     /lib/tls/i686/cmov/libnss_dns-2.7.so
b0755000-b0757000 rwxp 00003000 08:02 410625     /lib/tls/i686/cmov/libnss_dns-2.7.so
b0757000-b0759000 r-xp 00000000 08:02 375458     /lib/libnss_mdns4_minimal.so.2
b0759000-b075a000 rwxp 00001000 08:02 375458     /lib/libnss_mdns4_minimal.so.2
b075a000-b075b000 ---p b075a000 00:00 0 
b075b000-b0f5b000 rwxp b075b000 00:00 0 
b0f5b000-b0f5c000 ---p b0f5b000 00:00 0 
b0f5c000-b175c000 rwxp b0f5c000 00:00 0 
b175c000-b1763000 r-xp 00000000 08:02 473540     /usr/lib/libkrb5support.so.0.1
b1763000-b1764000 rwxp 00006000 08:02 473540     /usr/lib/libkrb5support.so.0.1
b1764000-b1787000 r-xp 00000000 08:02 473532     /usr/lib/libk5crypto.so.3.1
b1787000-b1788000 rwxp 00023000 08:02 473532     /usr/lib/libk5crypto.so.3.1
b1788000-b1816000 r-xp 00000000 08:02 473538     /usr/lib/libkrb5.so.3.3
b1816000-b1818000 rwxp 0008e000 08:02 473538     /usr/lib/libkrb5.so.3.3
b1818000-b1840000 r-xp 00000000 08:02 473412     /usr/lib/libgssapi_krb5.so.2.2
b1840000-b1841000 rwxp 00028000 08:02 473412     /usr/lib/libgssapi_krb5.so.2.2
b1841000-b185c000 r-xp 00000000 08:02 147742     /usr/lib/gnome-vfs-2.0/modules/libhttp.so
b185c000-b185d000 rwxp 0001b000 08:02 147742     /usr/lib/gnome-vfs-2.0/modules/libhttp.so
b185d000-b185e000 ---p b185d000 00:00 0 
b185e000-b205e000 rwxp b185e000 00:00 0 
b205e000-b209c000 r-xp 00000000 08:02 574673     /usr/lib/nss/libnssckbi.so
b209c000-b20a6000 rwxp 0003d000 08:02 574673     /usr/lib/nss/libnssckbi.so
b20a6000-b20e2000 r-xp 00000000 08:02 574670     /usr/lib/nss/libfreebl3.so
b20e2000-b20e3000 rwxp 0003b000 08:02 574670     /usr/lib/nss/libfreebl3.so
b20e3000-b2110000 r-xp 00000000 08:02 574672     /usr/lib/nss/libnssdbm3.so
b2110000-b2113000 rwxp 0002c000 08:02 574672     /usr/lib/nss/libnssdbm3.so
b2113000-b2176000 r-xp 00000000 08:02 473766     /usr/lib/libsqlite3.so.0.8.6
b2176000-b2178000 rwxp 00062000 08:02 473766     /usr/lib/libsqlite3.so.0.8.6
b217b000-b217f000 rwxp b217b000 00:00 0 
b217f000-b2183000 r-xp 00000000 08:02 230748     /usr/lib/xulrunner-addons/plugins/libnullplugin.so
b2183000-b2184000 rwxp 00004000 08:02 230748     /usr/lib/xulrunner-addons/plugins/libnullplugin.so
b2184000-b2188000 rwxp b2184000 00:00 0 
b2188000-b21c1000 r-xp 00000000 08:02 574671     /usr/lib/nss/libsoftokn3.so
b21c1000-b21c5000 rwxp 00038000 08:02 574671     /usr/lib/nss/libsoftokn3.so
b21c5000-b21c6000 ---p b21c5000 00:00 0 
b21c6000-b29c6000 rwxp b21c6000 00:00 0 
b29c6000-b29c7000 ---p b29c6000 00:00 0 
b29c7000-b31c7000 rwxp b29c7000 00:00 0 
b31c7000-b31c8000 ---p b31c7000 00:00 0 
b31c8000-b39c8000 rwxp b31c8000 00:00 0 
b39c8000-b39c9000 ---p b39c8000 00:00 0 
b39c9000-b41c9000 rwxp b39c9000 00:00 0 
b41c9000-b4229000 rwxs 00000000 00:08 2359312    /SYSV00000000 (deleted)
b4229000-b4238000 r-xp 00000000 08:02 375452     /lib/libbz2.so.1.0.4
b4238000-b4239000 rwxp 0000f000 08:02 375452     /lib/libbz2.so.1.0.4
b4239000-b426b000 r-xp 00000000 08:02 115665     /usr/lib/libcroco-0.6.so.3.0.1
b426b000-b426e000 rwxp 00031000 08:02 115665     /usr/lib/libcroco-0.6.so.3.0.1
b426e000-b429e000 r-xp 00000000 08:02 473406     /usr/lib/libgsf-1.so.114.0.7
b429e000-b42a1000 rwxp 0002f000 08:02 473406     /usr/lib/libgsf-1.so.114.0.7
b42a1000-b42a2000 rwxp b42a1000 00:00 0 
b42a2000-b42d2000 r-xp 00000000 08:02 473722     /usr/lib/librsvg-2.so.2.18.2
b42d2000-b42d3000 rwxp 00030000 08:02 473722     /usr/lib/librsvg-2.so.2.18.2
b42d5000-b42d7000 r-xp 00000000 08:02 375437     /lib/libkeyutils-1.2.so
b42d7000-b42d8000 rwxp 00001000 08:02 375437     /lib/libkeyutils-1.2.so
b42d8000-b42da000 r-xp 00000000 08:02 375409     /lib/libcom_err.so.2.1
b42da000-b42db000 rwxp 00001000 08:02 375409     /lib/libcom_err.so.2.1
b42db000-b4332000 rwxp b42db000 00:00 0 
b4332000-b4351000 r-xp 00000000 08:02 979270     /usr/share/fonts/truetype/msttcorefonts/Trebuchet_MS.ttf
b4351000-b4353000 r-xp 00000000 08:02 229527     /usr/lib/pango/1.6.0/modules/pango-basic-fc.so
b4353000-b4354000 rwxp 00001000 08:02 229527     /usr/lib/pango/1.6.0/modules/pango-basic-fc.so
b4354000-b435a000 r-xs 00000000 08:02 49031      /var/cache/fontconfig/945677eb7aeaf62f1d50efc3fb3ec7d8-x86.cache-2
b435a000-b435d000 r-xs 00000000 08:02 51660      /var/cache/fontconfig/e383d7ea5fbe662a33d9b44caf393297-x86.cache-2
b435d000-b435e000 r-xs 00000000 08:02 51512      /var/cache/fontconfig/e3fa16a14183b06aa45b3e009278fd14-x86.cache-2
b435e000-b4362000 r-xs 00000000 08:02 51352      /var/cache/fontconfig/921a30a17f0be15c70ac14043cb7a739-x86.cache-2
b4362000-b4363000 r-xs 00000000 08:02 51347      /var/cache/fontconfig/c69f04ab05004e31a6d5e715764f16d8-x86.cache-2
b4363000-b4367000 r-xs 00000000 08:02 54614      /var/cache/fontconfig/926e794c3d5e5dffcaf2fa83ef8d36c2-x86.cache-2
b4367000-b4368000 r-xs 00000000 08:02 51662      /var/cache/fontconfig/4c73fe0c47614734b17d736dbde7580a-x86.cache-2
b4368000-b436b000 r-xs 00000000 08:02 51350      /var/cache/fontconfig/a755afe4a08bf5b97852ceb7400b47bc-x86.cache-2
b436b000-b4373000 r-xs 00000000 08:02 51468      /var/cache/fontconfig/e3de0de479f42330eadf588a55fb5bf4-x86.cache-2
b4373000-b4395000 r-xs 00000000 08:02 50968      /var/cache/fontconfig/365b55f210c0a22e9a19e35191240f32-x86.cache-2
b4395000-b4399000 rwxp b4395000 00:00 0 
b439a000-b439d000 r-xs 00000000 08:02 51467      /var/cache/fontconfig/6d41288fd70b0be22e8c3a91e032eec0-x86.cache-2
b439d000-b43a5000 r-xs 00000000 08:02 51846      /var/cache/fontconfig/0f34bcd4b6ee430af32735b75db7f02b-x86.cache-2
b43a5000-b43a8000 r-xs 00000000 08:02 51351      /var/cache/fontconfig/de9486f0b47a4d768a594cb4198cb1c6-x86.cache-2
b43a8000-b43af000 r-xs 00000000 08:02 52040      /var/cache/fontconfig/d52a8644073d54c13679302ca1180695-x86.cache-2
b43af000-b43b3000 r-xs 00000000 08:02 49023      /var/cache/fontconfig/089dead882dea3570ffc31a9898cfb69
jos@hamerkeuh:~$