On Firefox 60, I'm still not on board with the newest versions after the support for legacy extensions was removed. SessionManager, an awesome (legacy, XUL) extension, still doesn't have a perfect equivalent in the Web Extension world. Tab Session Manager, which has similar functionality, seems to be lagging behind and struggling with issues in Firefox that prevent it from becoming a good session manager.
If there's one thing I could ask the Firefox team, it would be to focus on enabling web extensions to do almost everything that legacy extensions were able to. Without the power of feature rich and stable extensions, Firefox is currently inadequate for me (though I still use it as my primary browser).