Is that feature being out-of-the-box, as opposed to available through an add-on, really that important? I love Tree Style Tab (https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...), but I don’t really mind that it’s not built in to Firefox. It’s easy enough to install on a fresh computer, and the default tab bar is useable enough for short periods.

Anyway, as someone else said, setting browser.ctrlTab.previews to true in about:config should work. For me, it successfully changes the behavior of Ctrl-Tab to most-recently-visited order, and it causes hitting Tab while keeping Ctrl held to pop up previews of the tabs, just like Alt-Tab does on Windows. If you still can’t get that to work, there is also an no-restart add-on for what you want, MRU Tabs: https://addons.mozilla.org/en-US/firefox/addon/mru-tabs/.

I'm generally alright with add-ons that are Mozilla (or Google) 'branded', and those that are particularly well known otherwise. I also appreciate that the two you mentioned are listed as having been 'preliminarily reviewed' by Mozilla. I wouldn't go as far as to call the situation ideal though.

You're right about browser.ctrlTab.previews in any case - I must have only just tried option-tab, not restarted, or something similar when I responded to the other comment. How one is expected to dig up that option is a mystery to me though. Is it really such an unusual request?

Actually, this feature works out of the box in Firefox. You just need to turn it on by changing browser.ctrlTab.previews value to true in about:config.

Actually, I'm not sure that it does. Or perhaps I'm not adequately describing the behavior I'm looking for. Thanks in any case.

Can you explain why you want window manager features in your browser? If you use windows-in-a-virtual-desktop instead of tabs-in-a-window, they're LRU by default on pretty much every OS.

Because I rarely dedicate a virtual desktop to Firefox alone, and I enjoy the flexibility of a deeper hierarchy (virtual desktops - windows - tabs). Everyone has their own needs and usage patterns. Are you also opposed to file browser and terminal window tabs?

Unfortunately I cannot really justify my interest in philosophical or design-oriented terms. I had simply gotten used to the tab switching behavior in Opera, and have missed that behavior a great deal since having to switch (for reasons that should be obvious).