Hello,

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information.
Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Thank you.

Did do the Reset Firefox and it does seem to do the trick. But, I used that before 2 months ago with another issue and although it works, it it ofcourse not okay to do that reset every other month. Every time I then have to adjust my about:config settings (getting the good working old download window back, making the scroll speed to a normal good speed instead of the sloooow default setting, making 1 close tab button instead of that weird close button on every tab). Is there something to make a backup of my about:config setting?

I think this is caused due to cache size being so large, may be you can use some cleaners to cleaners to clear cache, next time and check if it is solved or else its one of your add on that causes this problem.

I have set my cache size to 350Mb maximum, so don't think that's a problem? Also, I have just a few add ons. One for lay out (LittleFox), one English dictionary and then I have Back/Forward Dropmarker and NoScript. I used to have also Adblock Plus but that slowed Firefox down a lot and caused some other problems. So haven't used that one for a while now. But I will keep an extra eye on the things you said and close this problem. Thanx for your input!