Hello Kirsi,
I regret for the inconvenience caused.
Once you uninstall AVG PC TuneUp, all the changes made by this application will be reverted back to original settings.
If the issue persists, then I suggest you to reinstall Mozilla Firefox on your computer and check if that fix the issue.
Today I got an offer to try TuneUp for free, and took it. When I tried to open Firefox after that, TuneUp kept telling me that Firefox is not in active use, and has been downgraded in priority. I uninstalled all AVG products, but Firefox still won't start. Which setting can I change to fix this? I have restarted to computer a couple of times after uninstalling AVG products. I am using WIndows.
Firefox does appear in the task manager after I've tried to turn it on, but the icon never changes to active status, and the window never opens…)
Kirsi, this was unfortunate to happen.
If you use AVG program in future, I recommend you not to uninstall it unless it was suggested from our end.
Kirsi, try restarting the service of Firefox browser.
Open RUN command by pressing Windows and R keys together.
In run window, type as "services.msc" without quotes and press Enter.
In services window, search for Firefox services.
Right click on and select "Start" or "Restart" whichever option is available.
Try accessing Firefox browser and inform the status here.