Hi, thanks for your comments and sorry to hear you're having trouble!

Regarding the deletion behavior: In general, Tab Stash is built with the expectation that any changes made to your groups should be explicitly done by you, not automatically. This helps to keep everything organized--my observation with other browsers and extensions has been that if groups are kept up to date automatically, it's really easy for tabs to get lost or irrelevant things to creep in. For example, if someone interrupts you to ask a question, and you open a new tab or re-purpose an existing tab to handle the interruption, that tab will show up in a group where it doesn't belong. Or worse, you will have lost something in your stash, just because you navigated away from the page you wanted to save.

There are also some technical limitations--Tab Stash stores everything as bookmarks, which are slow to update. If we were to keep your stashes in sync with every single change to your tabs, your browser would slow down considerably to handle all the bookmark updates.

So if what you are looking for is something closer to the "tab groups" features found in other browsers, I'm afraid Tab Stash won't be a good fit for you.

Finally, regarding restoring tabs: In order to re-open a tab which has been closed, Firefox itself must refresh/reload that tab from cache. This is entirely outside Tab Stash's control and is a necessary part of restoring the tab. You can avoid some (but not all) of this by telling Tab Stash never to unload hidden tabs (so the tab is still ready to go), but that comes at the expense of higher memory usage, and Firefox may still decide to unload the tab if memory usage gets too high.

That said, your point is well-taken that restoring a large number of tabs might slow down your browser, and we should probably show a warning to this effect. I'll keep this in mind for a future release!