hello, as this is sometimes a sign of active malware on a system, please also run scans with multiple other tools like the free version of malwarebytes and adwcleaner...

Troubleshoot Firefox issues caused by malware

Sometimes, those type of programs remove things you don't want removed. Always check the report before you let the program remove anything. When I run mine, it always wants to remove programs that I want to keep. Some of them I paid for.

Download Firefox Full Installer For All languages And Systems {web link} Save the file. Then;

Using your file browser, open the Programs folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Mac: Open the "Applications" folder. Linux: Check your user manual.

Look for, and rename any Mozilla and Firefox folders by adding .old to them.

Now run the full installer. If all goes well, remove the OLD folders when you are done.

maxb said

after running an adware cleaner I can't open firefox. No error message is shown; it simply pretends to be loading for a few seconds and then nothing. It does not appear in the task manager. I've tried to restart my computer and to reinstall firefox.

thanks a lot for your replies, Fredmcd and Philipp. I realised that I was able to open firefox in compatibility mode which was still not quite satisfactory. then I downloaded and ran malwarebytes and the problem was solved.

That was very good work. Well Done.