Could you try starting Firefox up in its Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features and some custom settings.

Hold down the Option key while starting Firefox. (Or if that doesn't seem to do anything, see this article: http://kb.mozillazine.org/Safe_Mode#Mac_OS_X)

A small dialog should appear, click "Start in Safe Mode" (not Reset)

Any difference?

Try to repair the disk permissions:

• http://thexlab.com/faqs/repairprocess.html

You can also try to uninstall Firefox (move to the trash) and reinstall Firefox.

Download a new copy of the Firefox application and save the disk image file to the desktop

• Firefox 30.0: http://www.mozilla.org/en-US/firefox/all.html

• Trash the current Firefox application (open the Applications folder in the Finder and drag the Firefox application to the Trash) to do a clean (re)install
• Install the new version that you have downloaded
• https://support.mozilla.org/kb/Installing+Firefox+on+Mac

Your personal data is stored elsewhere in the Firefox profile folder, so you won't lose your bookmarks and other personal data when you uninstall and (re)install Firefox.

• http://kb.mozillazine.org/Profile_folder_-_Firefox

Some problems occurs when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version)

• Remove Firefox from your program's list of trusted or recognized programs, then add it back. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}