Can you try to start Firefox in Safe Mode to see if Firefox opens properly with no error? You can start Firefox in Safe Mode below:

• Windows/Mac: Hold the SHIFT/Option key while opening Firefox
• Linux: Run firefox -safe-mode in the Terminal/Konsole

If Firefox opens up fine with no problems, it's probably one of your extensions that's causing the issue. You can re-enable your add-ons one by one until you find the one that causes the issue upon being re-enabled.

If the icon will not start Firefox, try to check it. Right click on the icon. Select Properties, then Shortcut. Make sure the link shown points to Firefox.

Thank you, but that didn't work either.

Remove the old icon, start Firefox. Then make a new link.

Try to repair the disk permissions:

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

Try to remove the Firefox plist file (org.mozilla.firefox.plist).

• http://www.macfixit.com/article.php?story=20060606082246983 How .plist files become corrupt and troubleshooting the results

Go to "~/Library/Preferences" and remove the plist file for Firefox (org.mozilla.firefox.plist)