It's another damned if you do, damned if you don't. FirefoxOS is regularly listed by commenters as an example of a wasteful side bet, whereas my feeling is more along the lines of yours, that it was striding greatly, as the saying goes, and attempting to be a major actor.

A big part of the market share loss was due to monopoly and distribution lockdown of a controlled platform tightly tied to hardware, so I can certainly see the strategic wisdom of the attempt. I suspect they didn't have the resources to press forward, they had a lot less money then than they do now. Which makes it all the more maddening that Yahoo's role as a partner was so muted; it could have made the difference for both of them.