Firefox 3.6.4 and above load plugins separately from Firefox, allowing Firefox to stay open if a plugin crashes. To make sure you are using the latest version of Firefox, see Update Firefox to the latest version.
Conflict with extensions
Firefox extensions can cause this crash. To test whether your crash is happening because of an extension, try launching Firefox's Troubleshoot Firefox issues using Safe Mode:
Click the menu button
, click help
and select Restart with Add-ons Disabled.... Firefox will start up with the Firefox Safe Mode dialog.
Note: You can also start Firefox in Safe Mode by holding down the shift key while starting Firefox.holding down the option key while starting Firefox.quitting Firefox and then going to your Terminal and running: firefox -safe-mode You may need to specify the Firefox installation path (e.g. /usr/lib/firefox)
In the Firefox Safe Mode dialog, click Continue in Safe Mode.