Comment 6 for bug 593225

Sorry for the long delay between communication. Sometimes Firefox profiles can become corrupt and/or extensions can conflict. Could you please try this with a new profile and see if the problem still exists? You do not need to delete your old profile to test. If a new profile helps, you might want to try to disable all your extensions and re-enable them one by one until you find the problematic one.
To disable extensions, Tools > Add-ons > Find the extension >
Highlight and click 'Disable' > Restart Firefox

You can start the profile manager with the following command:
firefox -ProfileManager