Sometimes, a document has multiple styles you don't need. At the moment, you have to perform the following on the Style sidebar: 1. Scroll to find one of a style to delete 2. Press delete or RClick and select Delete 3. Approve especially couple with the need to re-scroll, this is somewhat tedious. I would have liked to be able to select multiple styles and delete all of them at once. Note that this does not require the ability to apply multiple selected styles, nor edit them, update them etc. - those features can all be grayed-out when multiple styles are selected (or not, if someone happens to want to implement that).
IIRC, Thunderbird deletes the message tree if collapsed and just the selection otherwise. I'm a bit afraid of multi-selection as even when you disable function it still needs handling of drag and drop (organization) and double-click (apply). OTOH, this collapsed vs. expanded differentiation would be a hidden feature and maybe we better block interactions. Anyway, the request has been made before and should better reopened. *** This bug has been marked as a duplicate of bug 139824 ***