Simple Tab Groups for Firefox, I couldn't imagine using the internet without it. A bunch of Lemmy tabs filling up your tab bar and crowding out your normal tabs? Just make a new group and slap them over there, now all your other tabs are hidden in the other group and you can switch between them anytime.

I had one class where I needed like 10 tabs open all the time, I could just have them sitting in a different group so they didn't take up any space for my other tabs.