Usually less than a dozen, though I don’t quite see the relevance. I use MRU to switch between two to four (rarely more) related tabs.
In code editors I often have several dozens of tabs open, and MRU is a crucial usability feature when coding, so I’d say that its usefulness is independent of the number of open tabs.
In code editors I often have several dozens of tabs open, and MRU is a crucial usability feature when coding, so I’d say that its usefulness is independent of the number of open tabs.