Your profile may have become corrupted and may have to be recreated. First try starting in safe mode and disabling your plugins to see if the iproblem lies there. Press Alt+F2 and in the Run dialog box, enter firefox -safe-mode. Once you have made your changes, close and try restarting FF. If that works, you'll have to uninstall your plugins (probably in safe mode) and re-install them. If it doesn't work, create a new profile by starting FF with the --profilemanager switch. You'll need to make sure there are no instances of FF running before trying either option.
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“The people are my God” stressing the factor determining man’s destiny lies within man not in anything outside man, and thereby defining man as the dominator and remoulder of the world.