User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:80.0) Gecko/20100101 Firefox/80.0

Steps to reproduce:

I have smooth scrolling disabled (but still get smooth touchpad scrolling because I'm on Wayland).

After updating from the July 17th Nightly to the July 23rd, I get smooth scrolling for keyboard (space, shift-space, page up/down, arrow keys).

Also, this only seems to kick in after the browser has been running for a while. I couldn't reproduce it with mozregression.

 6:13.87 INFO: Last good revision: 76bbb83349bb0cb72b599611d5559707fd9a8d48
 6:13.87 INFO: First bad revision: 138e7b575614cbfc1e45576a15825f51cb6e6614
 6:13.87 INFO: Pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=76bbb83349bb0cb72b599611d5559707fd9a8d48&tochange=138e7b575614cbfc1e45576a15825f51cb6e6614

Thanks for reporting.

(In reply to Laurențiu Nicola from comment #0)

Also, this only seems to kick in after the browser has been running for a while. I couldn't reproduce it with mozregression.

You seemed to get mozregression working in the next comment. Did you find reliable steps to reproduce?

I can reproduce it easily using my old profile, probably because I have apz.allow_zooming enabled. I must have thought it was harder to reproduce it because of bug 1653796.

Does disabling smooth scroll work for you?

And yes, toggling apz.force_disable_desktop_zooming_scrollbars fixes it.

(In reply to Laurențiu Nicola from comment #3)

Does disabling smooth scroll work for you?

I hadn't tried yet when I commented. The reason I asked is that I was investigating something else with arrow keys yesterday and arrow keys didn't seem to go through a path touched by bug 1651332, so I was wondering if maybe there was some step I needed to take to make them. I was just trying to get as much relevant information from the reporter as possible before digging in.

Disabling smooth scroll seems to work like 90% of the time for me, 10% of the time (often the first scroll of a document) it's still smooth.

Bug 1655160 flipped the behaviour back off, so marking this bug disabled as of FF80.

The decision between smooth and non-smooth happens in ScrollToWithOrigin, which we don't get to with the new desktop zooming scrollbars code.

Patch here depends on the patches in bug 1658169 too now.

https://hg.mozilla.org/mozilla-central/rev/375219cab02b