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I bought a new computer (Dell Inspirion Laptop) for my wife. I had some trouble with installing Firefox and Thunderbird. I now get a message on each program: “

  • 7 Antworten
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  • Letzte Antwort von FredMcD

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I bought a new computer (Dell Inspirion Laptop) for my wife. I had some trouble with installing Firefox and Thunderbird. I now get a message on each program:

“Thunderbird (or Firefox) is already running but is not responding. The old Thunderbird process must be closed to open a new window.”

I also get “Thunderbird (or Firefoc) cannot be loaded. The profile may be missing or inaccessible.” I used control panel and uninstalled both programs. I also deleted the previous downloads of the program. I rebooted and went to the web site and downloaded the installation program and installed it. I keep getting the same response. Any help?

Alle Antworten (7)

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It sounds like your installations did not run through to completion. Did you start installing from scratch or after copying over Firefox and Thunderbird files from another computer?

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There is no firefox process shown so it can't be ended. When I hit close foxfire it then says it can't find my profile. No profile was created because it stops at "firefox is running". When I download and attempt to install firefox it says there was a prior version so I go in a big circle. I have uninstalled firefox but it still says there was a prior version which is the problem.

If could eliminate all traces of firefox I could download and install a clean version. Apparently the uninstall leaves some record that needs to be wiped out so firefox can load clean. How can I start over so firefox install doesn't detect a prior install. I hate to have to find a commercial alternative to firefox and thunderbird but at this rate I may not have a choice.

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Try this:

(1) Hide the Mozilla folder (data folder)

This is a hidden folder because it is in the AppData section of your Windows user profile. To access that, type or paste the following in the Windows 10 search bar:


That should expand to


Here, find the Mozilla folder and right-click it, then click Rename, then add OLD so it ends up as MozillaOLD. Or, if there's nothing valuable there, you could delete it.

(2) Remove the Mozilla Firefox folder (program folder)

Using Windows Explorer/My Computer (hold down the Windows key and press E to launch it) click into each of the following folders and see whether you can find a Mozilla Firefox folder:

  • C:\Program Files\
  • C:\Program Files (x86)\

If you find a Mozilla Firefox folder, you can delete it or rename it with OLD on the end.

Then try running a full installer -- if you have the small "stub" installer, you can download a "full" installer from this page:


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The system would not let me change or delete the only Mozilla files which were mozilla.browser files (01.94 KB) and some history file references. The message was that I needed permission from "system". I tried to change the ownership and/or permissions and it was not an option. The check boxes were greyed out.

After several hours I am going to give up and go to other products but thanks.

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Windows wouldn't let you rename or delete the folders I mentioned? That's very strange. Before doing anything sensitive on the system, I suggest scanning for any malware that might be trying to manipulate browsers.

Troubleshoot Firefox issues caused by malware

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And reboot the computer before and after the scans.