Open your task manager where it says Firefox.exe right click and choose to go to processes. In the processes, right click on Firefox.exe and choose to end process. Click on yes. Do this for any instance of Firefox running. Run a systems cleaner that gets rid of temporary internet files, etc. and then try to run Firefox again. It should work fine. After Firefox opens, go to your add-ons and disable all of them. Then re-enable them one at a time. After each re-enable, restart Firefox each time until the same problem occurs and that way the latest add-on you enabled will be the one causing problems. But it would be wise to do a RAM memory test to see if your RAM is okay. You can get a Memtest app here: http://www.memtest.org/. If that doesn't solve your issues then there are other ways: 1. Defragment your harddisk 2. Check your disk for errors by right clicking on your harddisk and under the tools tab select check for errors and check the box that says to correct problems. 3. Make sure Windows is fully updated. 4. Make sure your security software isn't prohibiting Firefox from accessing the internet.

A possible cause is security software (firewall,anti-virus) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/kb/Server+not+found
• https://support.mozilla.org/kb/Firewalls

See also:

• http://kb.mozillazine.org/Browser_will_not_start_up