Something changed

Out of the blue, I might be going crazy... but this website is the only one that's changed.

I logged on a couple days ago and noticed the font size is different or something about the fonts changed... and when I'm in my training log, it acts like my PC is 20 years old - as when I scroll down, it's no longer a smooth scroll, but really jumpy... it's hard to explain. I'm using Firefox... could it be something that changed in Firefox? I've recently updated my Java runtime, but it started doing this way after the update! I reinstalled Firefox, but the same thing happens!? Actually, as I type this, the font just looks different than what I'm used to! Is there a setting that I screwed up?