For everyone who are waiting for the official release, I already found a way to add this feature:For how to part, just check the post in GitHub: Firefox's Vertical TabsThis post is written in Chinese, you can use translator or just copy/paste the cod...
Better native vertical tabs with title bar (like in Microsoft Edge)
Already have this feature request post for vertical tabs, but I think with flexible space in Firefox, we can do better!
Currently, Tree style tabs can do make Firefox have vertical ...
