Since one of the latest updates, Firefox keeps randomly showing me a popup saying "pin this tab", pointing to a tab I just opened. I close it with its X button, but after a while it just pops up again. I don't want to pin a tab, ever - I have bookmarks for a reason and I don't see any point in this feature. How do I stop this incredibly annoying popup from bugging me constantly to do something I never want to do?