Could be an incompatibility with your graphics card drivers. Could you try disabling the use of hardware graphics acceleration in Firefox?

You usually need to restart Firefox in order for this to take effect, so save all work first (e.g., mail you are composing, online documents you're editing, etc.).

orange Firefox button or classic Tools menu > Options > Advanced

On the "General" mini-tab, uncheck the box for "Use hardware acceleration when available"

If you restart Firefox, is the issue resolved?

I unchecked the box and restarted Firefox but I am still getting the pixels.

Sorry to send you back to the options dialog a second time, but you might also test with Smooth Scrolling turned off.

Could you check whether you have any unrecognized extensions? It might be best to simply disable everything nonessential here:

orange Firefox button or classic Tools menu > Add-ons > Extensions category

Turned off smooth scrolling, no change. No unrecognized devices or outdated ones.

I did notice however after turning off the scrolling that the pixels are appearing if I am scrolling past images or videos, or if they're simply on the screen such as on Facebook. They no longer seem to just come at random but just around images or a site that has a lot of graphics in the background.

Ah, I think I may have found the problem. I checked my graphics driver and it had an update. After updating it and restarting my computer the problem seems to have gone away. Probably should have checked it sooner but I thought it was a browser problem since it was only occurring in Firefox. Thanks for your help!