Windows 10 bereikte EO (einde ondersteuning) op 14 oktober 2025. Als je Windows 10 gebruikt, lees dan dit artikel.

Windows 10 reached EOS (end of support) on October 14, 2025. If you are on Windows 10, see this article.

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Why do I get an error 21 notice when I try to uninstall Firefox betta?

Firefox
Xircal heeft 15 jaar geleden geantwoord
fionaomahoney@hotmail.co.uk
fionaomahoney@hotmail.co.uk

I was having problems with Firefox repeatedly crashing and decided to uninstall and reinstall. I'm a bit new to IT and installed MF 4.0 beta 11. I was told by my son that this is a trial version which I shouldn't really use until my knowledge is better. I tried to uninstall MF beta 11 but keep getting an error 21 notice. I installed MF 4.0 in the hope that it would uninstall the beta version but that hasn't happened. How do I get rid of the beta version?

I was having problems with Firefox repeatedly crashing and decided to uninstall and reinstall. I'm a bit new to IT and installed MF 4.0 beta 11. I was told by my son that this is a trial version which I shouldn't really use until my knowledge is better. I tried to uninstall MF beta 11 but keep getting an error 21 notice. I installed MF 4.0 in the hope that it would uninstall the beta version but that hasn't happened. How do I get rid of the beta version?

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Xircal
Xircal

Please do the following.

Go to Download Firefox 4.0.1 and download a fresh installation file to the desktop.

Then go to Add/Remove Programs in Windows Control Panel, scroll down to Mozilla Firefox and remove it, choosing to keep your bookmarks, customizations etc., (don't checkmark the box).

Then reboot and delete the folder called Mozilla Firefox at this location: C:\Program Files\Mozilla Firefox

Finally run the installation file you downloaded to the desktop earlier.

Your bookmarks, customizations etc., are maintained in a different location and will become available to you again once you complete the installation.

After you complete the installation, go to the Plugins Check page and update those if necessary.