I can partially duplicate the problem with gmail. It supports XLIST like mail.ru. However, when I unsubscribe (or subscribe) I don't see a discoverallboxes occur so the UI does not update to reflect the change. Collapse/expand also doesn't cause an update. However, on TB restart the UI change occurs (due to initial discoverallboxes URL) and the folder disappears (or appears for subscribe) as it should. So there seems to be a bug in TB that it doesn't do discoverallboxes on a subscription change with XLIST in effect. However, it appears that mail.ru is also not respecting the the unsubscribe either.
Bug 1759883 Comment 13 Edit History
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I can partially duplicate the problem with gmail. It supports XLIST like mail.ru. However, when I unsubscribe (or subscribe) I don't see a discoverallboxes occur so the UI does not update to reflect the change. Collapse/expand also doesn't cause an update. However, on TB restart the UI change occurs (due to initial discoverallboxes URL) and the folder disappears (or appears for subscribe) as it should. So there seems to be a bug in TB that it doesn't do discoverallboxes on a subscription change with XLIST in effect. However, it appears that mail.ru is also not respecting the unsubscribe either.