Comment 15 for bug 139875

But if you ran firefox in safe mode, all extensions (including Firebug) should be disabled.
In my case, uninstalling FireBug did not help (but I think it could have not uninstalled completely, because now I get at every firefox starup a window titled NS_ERROR_FAILURE with message:
  Componen returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIStringBundle.formatStringFromName]

MOZ_DISABLE_PANGO=1 works for me, the same with sudo firefox although there are the ugly solutions.

When I normally run firefox it segfaults (the number xxxx after the "line 131: xxxx" changes with every launch)

(gecko:23637): Pango-WARNING **: failed to create cairo scaled font, expect ugly output. the offending font is 'Arial 9'
/usr/lib/firefox/run-mozilla.sh: line 131: 23637 Segmentation fault (core dumped) "$prog" ${1+"$@"}

Attached strace