Vertical tabs / sidebar - expand on mouseover

[Wakkashamshay]

Vertical tabs/the sidebar would benefit from an 'auto-hide' or 'expand on mouseover' feature. Similar to how it behaves in Edge, I would like to be able to expand the sidebar for vertical tabs on mouseover when I want to review my open tabs. This would allow users to avoid manually toggling the expanded view and will improve the experience when tab groups are introduced.

[dsl]

Hi everyone, as a long time user of vertical tabs, I suggest reducing the default value of `sidebar.animation.expand-on-hover.duration-ms` from 400 to 100 ms.

It would be even better if we can explicitly add an input box in "Customize Sidebar" to set `sidebar.animation.expand-on-hover.duration-ms`, instead of having to discover about:config.

My justification is that this not only makes it more consistent with `sidebar.animation.duration-ms` (which is currently default 200 ms), but also because the 400 ms default is too slow. Based on human reaction speed, the on-hover animation should be no slower than the on-click animation because the user already expects what to happen on-hover. I used to share this frustration until I discovered the option in about:config, but I hope that future users will not have to go through this :).