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?