I like the new "Extensions" button so much, that I wanted to voice my support, and couldn't identify a better feedback avenue than posting to "Discussions."
In versions past, I ended up with a cluttered toolbar full of extensions, because I was tired of re-hiding them on each fresh Firefox install.
Hiding extensions wasn't saved across profiles/synchronized, so for those of us who change Firefox installs very, very frequently (ex., constantly rebuilding VMs/swapping devices), it was extremely tedious to hide every extension manually with each install. It would be great if going forward, extensions users un-hide/pin can be synchronized.
The only quirk, that others have voiced/seem frustrated about, is that the new button should be hideable. While this doesn't affect me, as I prefer having it easily accessible, it makes perfect sense why users would want that control.
Even when you like the new extension icon you still think it should be hidable - users should have option to set their browsers how they want. Thank you very much. See Firefox people? Please let us hide it, make the browser as we like it and are used to it and is comfortable for us. Browser - the most important program/application there is. And Firefox the best of browsers - except for some little frustrating detail - which this is now this one.