For nearly half a year I've had a very strange issue with a tab that simply vanishes. It's taken a while to notice and then figure out the pattern, and here's how it seems to go... I launch Firefox, which already has many open tabs; it's set to reopen my previous session. Typically I then open a new tab to check my email, do a DuckDuckGo search, or something else (but the activity/website doesn't seem to matter). Then something in my email or my search will inspire me to open a second new tab. All of a sudden when I do that, the first new tab of the session is gone. So for example if I was checking my email and saw something I wanted to research, I'd open a new tab and all of a sudden the email tab is gone. At least a few times I've then opened a *third* tab to go back to the website I just lost, and suddenly the vanished tab will reappear, and I'd then have duplicate tabs on the same website. Much more often the vanished tab does not return until *later.* That is, I eventually close Firefox and eventually reopen it, and suddenly there it is again. I believe, but I'm not certain, that this *always* causes the vanished tab to reappear. It's a pain to rely on this fix, though, especially since it can take something like 20 seconds to reload all those tabs. I think this strange behavior only happens when I first launch Firefox -- in other words, only once per session. I've never noticed it hapening a second time in the same session. I can freely open new tabs without fear of losing another (at least none that are in the visible part of the tab row). Anyone else have this issue? Or can you recreate it?