For decades, one of the best thing about Thunderbird (compared to the primary offering from M$), is that Settings are well organized in a single hierarchical tree: if you get to the bottom of the list, you either found the setting, or it doesn't exist. Whereas in OL it's hidden under 'special'/'advanced'/'extra' or some other useless label, and likely to be moved to an other hidden location with every new release.
Do users really change from TableView to CardsView so often that it needs a permanent button in the message-list header? I guess you can't take it away now. But when a user of several decades has to do a web search to figure out how to get the standard table-view back, there's a problem. This should have FIRST gone into MenuBar/View, and if it needs it's own button, well fine, but NOT before you make it accessible from the MenuBar. I shouldn't have to search the entire UI for well disguised glyphs that only give up their purpose after a mouse-hover.
