If this only happens if you try to restart Firefox another time after you have closed Firefox, see:

• "Hang at exit": http://kb.mozillazine.org/Firefox_hangs
• "Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs

Use "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit) to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

See also:

• http://kb.mozillazine.org/Profile_in_use
• https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding

Previous version worked OK. Since removing version 29.0 and going back to 28.0 works perfectly.

Caution

Comment by a moderator (~J99).
Please be aware that downgrading to an insecure unsupported version of Firefox is not going to be recommended. If necessary you would be better off using a secure alternative browser. (Corporate users with such an issue will probably opt for ESR )

Obviously if this is a Firefox bug it is going to be fixed as a priority.

Please see my post:

https://support.mozilla.org/en-US/questions/997448

Thanks.

Hi jenoseeel,

By the way do you use any Norton related Software ?
If so does temporarily disabling that help ?
(If you see the problem whilst offline you do not need to risk going online with Norton related software disabled.)

You could have a similar problem to some of these others or it may be a different problem. We do seem to be starting to get an idea of what causes at least some of these problems but we are looking for more help and information.

Obviously for security reasons it is good to avoid using Fx28 now where that is possible.

• Install an older version of Firefox
• https://www.mozilla.org/security/known-vulnerabilities/firefox.html

Troubleshooting

If you are interested in trying to fix the problem with your Fx28 and trying to investigate the Fx28 problem you may be interested in reinstalling Fx29 as an additional custom install in addition to Firefox 28.

You may find one or more of these steps is a workaround to prevent the problem:

• Setting Fx 29 so that history or cookies are not cleared on close down.
• Disabling all addons
• I also noted someone else suggested trying "privacy.sanitize.sanitizeOnShutdown" on and "network.seer.enabled" off for testing purposes?
  ( Described as a wild guess but will be an educated guess based on known changes to Fx 29 - netpredictions.sqlite )
• Installing additional versions of Firefox is covered in this article
  http://kb.mozillazine.org/Testing_pre-release_versions#Installing_multiple_versions

Further information can be provided for anyone wishing to try any of this.

It is understandable if you do not wish to try this, however only some people see this problem, and so we need to try to get more information from those with the problem so that it may be investigated and fixed.

I will leave this here as it may be of interest to others who read the question. Before doing anything though you may wish to look at Compumind's thread as that is likely to have the latest information on the problem.

Pardon me for butting in. For Windows users, I have written a Windows DOS batch file that will close Firefox if it locks up on you. This is not a cure but will make it easier if Firefox locks up.

I do not have Norton on the computer - I use MSE.

Something that worked in a similar case was to turn off a particular new database. You do this by using about:config to change a particular preference.

Try this

1. Key into the addressbar about:config ; hit Return, accept any warning
2. You are looking for network.seer.enabled
   Keying into the search filter seer should bring up the pref.
3. Right click and Toggle the pref network.seer.enabled to false
4. similar actions will reset it if it fails to help.

• See http://kb.mozillazine.org/About:config

Jenoseel,

Firefox 29 updates tomorrow and has a fix for some problems, including a fix that helps with hangs. I suggest you make sure you are back on Firefox 29 or you will miss the fixes.

If you upgrade wait for the version Firefox 29.0.1 and then post back again with whether or not it is now working.