If Firefox is still frozen, you might need to "force quit" Firefox. There was an earlier thread about how to do that: I cannot Quit Firefox on my Mac. This means I can't shut down my computer and I cannot install updates.

Of course, Firefox might still have a problem the next time you start it up if it is freezing based on something on the site you're viewing. But it's worth a try.

Before trying a Reset, you could test in Firefox's Safe Mode. That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. This article has more information about how to use it: Diagnose Firefox issues using Troubleshoot Mode.

Any improvement?

This didn't help. My first error message was there was an unresponsive script. Anything I clicked on did nothing and I can't even access Troubleshooting Firefox. I appreciate your suggestions, but they didn't wok.

Were you able to force quit Firefox and start it up in Safe Mode? Where did that go wrong?

Can you start Firefox in Safe Mode by holding down the Options key?

Try to download the full version and trash the currently installed version to do a clean install.

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

• Firefox 32.0: https://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

You can also try to boot the computer in Safe mode. Starting up in Safe Mode: http://support.apple.com/kb/HT1455