Now this is interesting. My media server, a different PC than the one above doesn't have the same issue with Firefox. All the speed tests are pretty much the same between browsers. I hadn't had it hooked up for a few weeks because I'd been using an Amazon Firestick instead but I plugged it in for this test.

It's a little bit newer but has a Core i3 and double the RAM.. 8 vs 4 Gigs but I don't see how either of those things would make a difference in speed tests. Both have fairly new SSD's for the main OS drive.

Firefox version is the same on both computers.