I was a long-term holdout on 3.6.x and finally made the jump. I've found enough add-ons & plug-ins to make 11 look as close to 3.6.x as reasonably possible, but with one singular (and grating) exception:
Does anyone know how to recreate the Tab Mix Plus behavior where I could get a New Tab button on the far left side of the Tab Bar? Yes, I know I can double-click or middle-click, but I want my New Tab button in the exact same spot it's been for years.
It is one of the blessings of old friends that you can afford to be stupid with them. Ralph Waldo Emerson.