It also works on Firefox (and on Linux); if you use split address/search bar it focuses to the search bar instead as it used to be.

Indeed, I normally turn off "keyword.enabled" and "browser.urlbar.oneOffSearches" in about:config.

Yes, you need keyword.enabled set to false otherwise Firefox will still search even though you have a different search box :(.

In Firefox, it is also possible to set keyword.enabled to false and still search explicitly in the url bar via the keyword search mechanism (they overloaded the terminology a bit :/, the one if you right click on a search box and select "add a keyword for this search"). I've been thinking of trying to just use DDG style ! keywords via the url bar (and s for a default search to make it easier to type, maybe single letters would be easiest in general) rather than a search box. OTOH, the keyword search (the second type :/) seems neglected and I wouldn't be surprised to see it disappear at some point.

That works on multiple platforms! I'm able to do that on Arch.

In the good old times, ctrl-l went to the location bar and ctrl-k went to the search bar. After they merged, ctrl-k just prepends the question mark. But... as an old shortcut, pretty much everything supports it.

Isn’t “?” and ctrl-k the same number of keystrokes?

Only if you don't count your mouse clicking the omnibar as a keystroke.

That’s a good point. I didn’t consider that, and now I’ll use this shortcut. If I had been at my computer I would have realized that immediately.