alt Hacker NewsFor peak usability, Windows 3.1 kept the mnemonics underlined _all the time_. It's been downhill since then. Though I'm looking at the menu bar on Firefox on Ubuntu right now and at least the mnemonics are underlined now as I type, even without hitting "alt".
Oh, man, I had forgotten about having the menu keyboard shortcuts underlined all the time. Sometimes you could even tell that whoever had a sense of humor in choosing the mnemonics. I don't even know how to open the macOS menu bar without my keyboard now.
After doing an Internet search for it, I have learned that it is Fn-Control-F2, after enabling Full Keyboard Access in Accessibility. How could it get this bad? (Apple's other accessibility features are amazing.)