Yesterday, as I was reading a page, the little "motion icon" showed up, refreshed my screen and reverted it back to the original magnification. I figured it was something I did so I re-magnified it and within a minute it reverted again. It's been happening ever since and only on Firefox BUT not as I am typing this message!!!
When I move to a different thread, it ups the magnification to where I set it but within a minute, it reverts it back to original again.