In my case, it was like the brakes were dragging, but now they are not.
Probably doesn't help that after 9 years with the same mode/router, we just got a new one. Definite speed change after that (easily 5+ times faster). So maybe I didn't notice the Firefox speed change when it happened because we were still using a crappy old router.
__________________
.
Rhymes with slice, rice and mice, and probably should be spelled like "Tice."