Hard-/Software

1. Trackpad on Macbook Pro Mid 2015
2. macOS 10.14.5
3. Firefox 69.0a1 (2019-05-25), Build ID 20190525093913

Steps to reproduce

1. Go to any page where you can scroll vertically, e.g. https://bugzilla.mozilla.org/show_bug.cgi?id=1441308
2. Scroll down and let go of trackpad while page is still in motion (scrolling)
3. Touch trackpad while page is still in motion (scrolling)

Expected Behaviour

Page stops scrolling in the moment when user touches the trackpad.
This is still the case with e.g. Firefox 68.0b4

Actual Behaviour

Page keeps scrolling even after touching the trackpad again.
User has to move (minimally) in opposite direction to force a stop of scrolling motion.

Regression

This seems to be a regression of bug 1213601, see Pushlog:
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=292f7a045dac73573103c9d07cd3f222109ff047&tochange=f9699ae30f4d5256b6af7c8493e84984aadb4568

If it affects mac it's not a Gtk bug :)

There weren't that many changes to the APZ code.

https://bugzilla.mozilla.org/show_bug.cgi?id=1213601#c40 — maybe the addition/subtraction thing has something to do with it.. (though apparently that was introduced because of android)

or mSimulateMomentum is somehow not false? (bitfields are initialized to zero, right?)

Bitfields are not auto-initialized, fwiw.

I think we should probably back out bug 1213601 until we figure this out.

This was fixed by the backout of bug 1213601.

Please test the try build https://treeherder.mozilla.org/#/jobs?repo=try&revision=df5b5ab1175101453210f87f24dae1c74e099915&selectedJob=249048268 (job details → target.dmg in an "OS X" build I guess)

(In reply to greg v [:myfreeweb] from comment #8)

job details → target.dmg in an "OS X" build I guess

Yes it is! Thanks, wouldn't have found it :)

Tried a few pages with that build and scrolling works perfectly normal 👍