If you "kill" the firefox.exe process in the Windows Task Manager and try again, does it behave any better?

You can open the Task Manager by pressing Ctrl+Shift+Esc.

Then click the Processes tab. You may need to click the first column heading to alphabetize the list if firefox.exe is hard to find.

Then you can select firefox.exe and click the End Process button.

(You might want to minimize this dialog for quick access while doing the following tests...)

In case there is a problem with your home page, you can start Firefox up to a blank page from the Windows Start menu search box by pasting the following and pressing Enter:

firefox.exe "about:blank"

You also can try starting Firefox in its Safe Mode. Hold the Shift key down while double-clicking your Firefox program icon.

In the small dialog that should appear, click "Start in Safe Mode" (not Reset)

More info: Diagnose Firefox issues using Troubleshoot Mode.

It is also possible that your security software (firewall, anti-virus) 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

• https://support.mozilla.org/kb/fix-problems-connecting-websites-after-updating

Hi Jscher2000. Thanks for your response. Unfortunately nothing has helped.

1) Firefox.exe does not appear in the processes list in task manager.

2) I tried to open Firefox from Start Menu Search. Again did not start.

3) I tried starting in safe mode as you suggested. I had tried this before but

   sadly the result is the same - not starting.

Are you able to ofrfer any other suggestions? Thanks

Hi cor-el. Thank you for your contribution. I have done as you suggsetd and removed anything related to Firefox but Firefox still does not open. I tried adding firefox to the list but again still does not start.

Do you have any further ideas? Thanks

If Firefox is starting and then exiting (not hanging and lingering in the Processes list) it could indicate that the installation of Firefox is damaged. In that case, re-running the installer might help. This usually does not affect your settings.

https://www.mozilla.org/en-US/firefox/all/ (scroll down to your language)

It's also possible that an external process is terminating Firefox.

• Some security software might do this, as noted in cor-el's post above.

• Also, some malware may do this, so you may want to run some supplemental scans. This article recommends free tools for that: Troubleshoot Firefox issues caused by malware.

Hi Jscher2000. I have tried to re-install firefox several times previously but tried again anyway. Did not work. I have run the Microsoft Malicious Software tool but nothing was found. I just cannot understand what is going on. It used to run quite happily. When I click on the icon a round circle appears for several seconds then disappears. That's all. Any other ideas please. Thank you.

Hi PuzzledUser, is the Microsoft Malicious Software tool the one that comes with Windows updates from time to time? You may want to try some of the others as well.

There is a folder you can check to see whether Firefox is creating crash reports. That's described in the last section of this article: Troubleshoot Firefox crashes (closing or quitting unexpectedly). Perhaps Firefox isn't running long enough to create a report, however.

Hi Jscher2000. Thanks again for responding. Yes the Microsoft Malicious Tool is the one which often comes with Windows Updates andcan also be downloaded from the Microsoft Website which is what I usually do. Aftewr send ing my previous reply I downloaded anotyher Malware Removal Tool (IOBit). After running this, to my disbelief it found 66 problems which I repaired. Sadly I still cannot open Firefox. I follwed your suggestion re crash reports. Sadly the last report was in July 2012 so again mot helpful. I am wondering as I recently updated Firefox if this has anything to do with it? Unfortunately I had deleted the previous versions thinkung they might be clashing. I am wondering whether it is poossible to download a previous version frok Mozilla?

You can download Firefox 23.0.1 using a link in this article: Install an older version of Firefox. You'll see the security warnings there, of course.

Hi jscher2000. Sorry for they delay in getting back to you, I have been away for a couple of days. Anyway I decided to have another go before saw your last message. I do not know why but has suddenly as it stopped working it has now started working. Quite honestly I don't know for sure what the problem was. I happened to go into Task Manager and spotted Firefox listed as you advised earlier but I am sure was not there at the time, and deleted and tried again and it is now working. It will have to remain as one of life's mysteries! Thanks again for your help.

It is possible that your security software got updated and now recognizes and allows the current Firefox release.