So I had to reinstall Win10, So a fresh install with Firefox and a new profile (I imported bookmarks). And now everything is sluggish. Videos and .gif are fine, but the UI is lagging. If I open and close tabs I can clearly see them stutter, before it was fluid movement. It's the same if I zom an image (the images get larger and "pops up") I can see it stutter. Same with right click, it takes a moment before it opens.

It was working fine before, but now it's not working properly. I tried to create a new profile and reinstall Firefox, with and without addons, but didn't help.