You can get something somewhat similar to Firefox Focus in regular Firefox for Android by enabling the option to open in Private tabs by default and turning on

You can get something somewhat similar to Firefox Focus in regular Firefox for Android by enabling the option to open in Private tabs by default and turning on tab auto-closing. That's what I did for a while when there were indications that Firefox Focus was about to be abandoned (which never actually happened). Even better though, now that Add Ons are opened up on Firefox for Android you can install Cookie AutoDelete. Then you just use regular tabs and can keep your Kagi cookies (and any other sites you regularly log into) but have it nuke every other site. There is also a Kagi Add On. It didn't do pretty much anything when I first installed it last year but it might work these days. Oh, and finally, there is the Kagi Session Link you can use that embeds a token in the URL so that you can more easily use it for something like a search provider in Incognito/Private tabs.