[dctoedt]

Seems to do this in Microsoft Edge, too.*

* I use Edge bcs of the vertical tabs — Safari's equivalent is a poor substitute. Firefox didn't seem to have vertical tabs last time I checked.

[anana_]

They do now - https://support.mozilla.org/en-US/kb/use-sidebar-access-tool...

[zacblanco]

https://www.firefox.com/en-US/features/vertical-tabs/