I’m experiencing this as well, using FF 77.0.1 (not Private Browsing) on MacOS - Catalina.
All pages of the docs - once the scroll is roughly 2/3 down the page, the page jumps back to the top.
I’ve tried “sneaking” down the page by scrolling reeeeally slow, but looks like there is a point where a jump back to the top is triggered no matter what. The page will not reach the bottom and stay there.
For different doc pages, the point seems to change. As in, some pages (shorter pages from what I can tell) I’m able to make it almost to the bottom/footer before it jumps back up. Longer pages, it’s usually about ~2/3 - ~3/4 of the way down that triggers the jump back up.
Been trying to find a work around for a few days now but so far, nada.
Safari seems fine, I can scroll all the way down and stay there with no issues.
I do not have Chrome installed at this time.