Balance timeline zooming sensitivity between Firefox and Chrome

[fbarl]

Resolves #2768.

If this will behave nicely, consider extending the same logic to #2787.

[rndstr]

This still has a large discrepancy in sensitivity between FF (lower) and Chromium (higher) for me.

A line-to-pixel ratio in the area of 35 puts it at about the same sensitivity. This would be roughly double what you suggest so maybe there is some fast-scrolling setting in effect for your env (https://stackoverflow.com/a/37474225 suggests that Windows uses 2x).

[fbarl]

@rndstr After reading about this more, I came to conclusion that any attempt to balance the cross-browser sensitivity perfectly is futile because it will always depend on the platform and some special settings.

Although we seem to be using very similar browsers/environments, line-to-pixel ratio for you seems to be 35px while for me it's 15px. I changed it to 25px in the code and I'd say that if the real sensitivity on browsers will be +/- 50% from that value, that will still result in a good UX.

[rndstr]

@fbarl that makes sense to me.

Maybe cross-check with @rade once deployed since there is the possibility that I'm an outlier with the ~35px. I do have unconventional settings atm due to hidpi/lodpi monitor combo that FF could pick up. Will revisit once that is gone.