Pinned tabs in Firefox are lacking real wolrd functionality. Firefox should copy Safari pinned tabs.
The best example of pinned tabs functionality on web browsers can be seen on what MacOS Safari is doing. Safari maintains pinned tabs across multiple windows and sessions, it also remembers the initial url used when the pin was placed, that means that when you open a new Safari session, the pinned tabs will always display the url you pinned and not the last page you visited on that tab. Firefox pinned tabs lack real world functionality, this point can be proven by seeing how many Firefox extensions for specific sites are on the extension browser. Please add this functionality, it could be one optional preference on the Settings page.
Opaite Mbohovái (3)
I suggest you post that on the feedback/ideas site. Help > Share Ideas and Feedback.
Rob said
Safari maintains pinned tabs across multiple windows and sessions...
Do you mean every time you create a new window in Safari it duplicates all the pinned tabs into that window?
Interestingly, it does not. Safari maintains the pinned tabs as unique instances across different windows. So lets say you have YouTube as a pinned tab, then you open a new window. That window also has the same pinned YouTube tab and it's the same tab instance as the first window. Also, when the user has the same pinned tab open on different windows, it only keeps one of those pinned tabs active and the other is automatically deactivated.
Moambuepyre Rob rupive