Scroll container width keeps increasing on mouseout on Firefox 61 on Mac

[davkal]

The broken behaviour is described here: https://github.com/grafana/grafana/issues/12726

I think we're hitting a FFMAC special case in baron, our scroll handler. It adds padding (15px) on each scroll element update: https://github.com/Diokuz/baron/blob/master/src/core.js#L596

The update here is triggered on an animation or transition event on hover: https://github.com/Diokuz/baron/blob/master/src/core.js#L209

To verify, you can change your user agent to not match the regexp in https://github.com/Diokuz/baron/blob/master/src/core.js#L46 and the issue disappears.

My guess is that baron no longer needs this special treatment in FF61

[ViViDboarder]

@davkal I wrote a patch (referenced in this PR), but want to verify it. Any idea how I can reproduce using the test page? I'm not quite familiar enough with what Grafana is doing to create a good test.

I'm looking at test/index.html and none of the test examples seem to reproduce the issue, even on master.