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Firefox will not start. I've tried rebooting multiple times. Windows 7 Pro; I dbl click and nothing happens. It was fine yesterday.


Firefox will not start. It worked fine yesterday and for months. I was changing some settings for being able to view hidden files in a couple directories. Rebooting does not help.

Additional System Details

This happened

Every time Firefox opened

This started when...

I was changing some settings for being able to view hidden files in a couple directories.


  • User Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E; BRI/1; InfoPath.3; AskTbORJ/; BRI/2)

More Information

  • Top 25 Contributor
617 solutions 4264 answers

Hello PingPilot,if you can't switch the changes you already done in previous state then try the Reset Firefox – easily fix most problems with this solution, Firefox create a new profile (your old Firefox profile information will be placed on your desktop in a folder named "Old Firefox Data") and restoring Firefox to its factory default state while saving your essential information(Bookmarks, Browsing history, Passwords, Cookies, Web form auto-fill information)

BUT the following items are either NOT SAVED or set to their defaults : Extensions and themes, Open tabs windows and tab groups, Site-specific preferences, search engines, personal dictionary, download history, DOM storage, security certificate settings, security device settings, download actions, plugin MIME types, toolbar customizations and user styles.

How to start Firefox in Safe Mode

thanks you

Modified by ideato

Question owner

Your solution assumes that I can start Firefox to reset it. That's the point, it won't start. I double click on the shortcut (even tried dbl clking on the exe in the explorer) and it does not open, execute, start; whatever you want to call it. I see the litte icon for a program about to start and NOTHING opens, starts, etc.

  • Top 10 Contributor
  • Moderator
10783 solutions 97050 answers

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.


Helpful Reply

I've tried turning off the firewalls, no luck. I found the article on crash reports and actually found a crash report from this morning. (Not yesterday when the problem started) I tried going to http://crash-stats.mozilla.com but it won't come up using IE9. I tried attaching the Crash Dump File, as suggested and still no luck. After a full day of trying things to restore Firefox, wouldn't it be faster to just uninstall and reinstall?

Question owner

Problem Solved. The issue was a file called parent.lock. Apparently I had closed Firefox incorrectly or inadvertently and this file locks the profile, causing Firefox to think that it's already running. Deleting this file solved everything.