If anybody else is hunting for this:

Hamburger menu -> Help -> About Firefox

Your version number is listed under the big heading, and if there’s an update available there should be a button next to that.

My question, I'm on beta channel and updated to 68.0b11 today and don't see detailed release notes.

67.0.3 (normal channel) lists "Security fix" https://www.mozilla.org/en-US/firefox/67.0.3/releasenotes/

But beta channel only says 68.0beta released May 22nd, no info on newer beta versions. This is the link in the about box: https://www.mozilla.org/en-US/firefox/68.0beta/releasenotes/

I totally get not wanting to write fine grained release notes on every single beta version, but 0-day fixed feel the kind of thing that ought to be explicitly pointed out. I'm assuming that the same fix from release channel was also pushed in the 68.0b11 update but a release note about that would be swell.

On mac, it's Firefox menu -> About Firefox, then wait for it to download the update and click restart

The quickest way is and always was Help > About Firefox

Can't really test from my phone, but isn't pressing and releasing the Alt key still a shortcut for displaying a menu bar if one exists?

Yes, on Windows.

Are there not comparable or identical shortcuts for keyboard users on most nix boxes and Macs? I admit to not being up to speed on Command/Option/Splat Mac shortcuts, but I wouldn't have expected the chrome to diverge that much between systems from a common code base.