Several of you have noticed the lack of Double right click in the public beta, and Nathan Freeman pointed out how to turn it on via some magic setting.
After conferring with development, I entered a bug report to re-add the preference.
It will not work in all windows. It will not work for the spreadsheet, presentation or document tabs, or the embedded browser.
This means that it is inconsistent, and the inconsistency pained me greatly. However, here's the rationale: Only the advanced users know about it, and several of you have said you'd rather have it for some tabs rather than no tabs. Most (un, ALL??) business users are unaware of this preference and most likely will not be perturbed by this inconsistency. This is exactly the kind of compromise I wanted to avoid. I feel soiled, dirty, a bit like a politician....