Hi David, for quick reference, you can re-open a tab using Ctrl+Shift+T, or right-click any open tab and use Reopen Closed Tab. If it was the only tab in the window, so the entire window closed, you may need to use Ctrl+Shift+N or in the most extreme case, restart Firefox.

Yahoo users have been reporting something similar, but I'm not sure the exact cause/solution has been identified. Does AOL now use the Yahoo platform for mail?

I know that it's easy to reopen that tab, but it is really annoying to have to do so.

I have no idea what the relationship is between Yahoo's mail client and AOL's. I mean, they are owned by the same company, but do they use the same coders and have the same platform? I haven't been on Yahoo in years.