I usually have three tabs pinned for easy access. Upon using the new "add tab to taskbar" feature though, there's a problem.

If I use the button to pop out youtube music for example and then close the version of the browser that it came from, and that my pinned tabs are on, any subsequent times I try to open firefox won't keep the tabs pinned. This also happens if I attach youtube music to my taskbar permanently and try to open it from there and then try to open firefox regularly.