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class not registered error

New Contributor

class not registered error

i have been using firefox as default browser for a long while.suddenly i am confrinted with "class not registered" when I try an open a link from my email.I am usung version 20.0.1 I have followed the instructions on your site to no avail. i have delted mozilla from program file etc and reinstalled with no good result. Effectively i am now not able to use Firefox anymore as my default browser.. surely, there must e a solution to this problem

Site Moderator

Re: class not registered error

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

  • Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.

You can also check for issues caused by plugins:

You can try to rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default values.