Random guessing ...
If you have not already - turn OFF your Mac, wait - no more than one minute, and then turn it ON. Now try opening (launching, running) 'Firefox', 'Mozilla', 'Opera', etc. Any difference?
If not, quit the web browser applications, and place each application's '.plist' ['org.mozilla.firefox.plist' and 'com.operasoftware.Opera.plist'] file (from the '~/Library/Preferences/' folder) and the 'Mozilla' folder (from the '/Library/' folder) - onto the 'Desktop'. Try opening the web browsers each again. Any difference? If so, you will have to configure the various web browser's settings, again.