On the tree style tabs part, I wish Firefox had better hooks for vertical tab extensions (like TST) to use than the multipurpose sidebar. I’ve not once used the

On the tree style tabs part, I wish Firefox had better hooks for vertical tab extensions (like TST) to use than the multipurpose sidebar. I’ve not once used the sidebar for anything but vertical tabs and it’s a nuisance to have to hide the unnecessarily huge sidebar header with usercss. Letting approved addons hide the default tab strip would be nice too. It’s not like vertical tabs are that strange of a feature at this point… Vivaldi, Edge, and Orion have them built in and they’re the only option in Arc. I understand why Mozilla might not want to have to deal with maintaining a full vertical tabs feature themselves but at least give extension authors the tools they need.