I forgot about TMP. Even so, that's still not a ton of users in terms of the total Firefox users. Plus, I'd wager a large percentage of those are TMP legacy users. Way back in the day, TMP was the only way to properly manage sessions and tabs. Firefox now has full session management and you can reload, pin, undo close, close other tabs, and move tabs around to your heart's content. Heck, the most recent review of the extension even says as much.