Firefox 157 broke my vertical tabs

Only a few weeks ago I was singing the praises of vertical tabs and specifically threw praise at Firefox's implementation, when coupled with Tab Groups (for combining tabs into a collection that can be moved together, folded-away and restored later) and Multi-Account Containers (which allows tabs to have isolated browsing contexts, which is great for privacy and also helps a lot with logging into multiple accounts simultaneously). At the time, my tabs looked a bit like this: But this week Firefox 157 came out and messed it all up. Specifically, the problem is that the new UI engine Nova - with its insanely-rounded corners and space-gobbling design - in a single stroke made my sidebar significantly less-usable. I followed Mozilla's recommendation and installed the Proton theme, which aims to make the browser look like it did back under the Proton UI... but it doesn't really cut it. Take a look at the exact same tabs today: So now I guess I need to teach myself enough about Firefox…