Update all plugins, uninstall any plugins you no longer need or disable all plugins, to see if that resolves the problem.See Issues related to plugins for plugin locations and additional troubleshooting information, including how to disable plugins if your browser will not start.
For detailed Firefox instructions, see Standard diagnostic - Firefox#Clean reinstall.
This error is caused by inconsistent file versions ("application.ini" and/or "platform.ini" and possibly others).
The problem may be a security program such as Zone Alarm Extreme Security (see below) that is preventing changes to your Mozilla application files after an update.
If the browser starts when you run it in Safe Mode, it's likely that an extension or, in Firefox 4 and above, hardware acceleration is causing the problem.
See Problematic extensions and Firefox crashes#Extensions for more information.
Depending on your browser version and OS, Firefox or Sea Monkey may hang, crash, or simply fail to start because of a problematic plugin.
If possible, visit Mozilla's Plugin Check page with another browser that Plugin Check supports (e.g., Safari or Opera) to help identify installed plugins.
If the Firefox or Sea Monkey browser process from the previous session did not exit properly, the next time you attempt to start your Mozilla browser it may fail to start with no error messages.
Attempts to restart the browser may result in multiple instances of Firefox or Sea Monkey in the processes list.
You will not be able to start the browser until you first end all browser processes or restart the computer.
(If this is a recurring problem, read this for other possible solutions.)   Try starting Firefox or Sea Monkey in Safe Mode (see the linked article for details).