It may be a bot, UA switcher, some old fork, or perhaps someone has found it in random reddit thread and overridden default UA years ago.

WebKit–based Firefox iOS browsers do not use "Firefox" as the product bit, for pretty much this exact reason.

This is not, and never has been a Gecko–based Firefox UA. (See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/User-Agent/Firefox for the canonical source.)

This looks like some "randomizer" extension trying to resist fingerprinting by scrambling the bits, but mostly looks like a chromium–based UA, like a Brave or Opera would use, with something messing with the product trailers.

This bugs me. My first guess would be that a Webkit based Firefox could not be qualified as really Firefox. Although that, I could imagine a Firefox for iOS or MacOS based on Webkit, may be,

Firefox on iOS/iPadOS is a shell for webkit due to Apple's restrictions on what browser engine can be used though in some certain markets now due to a court ruling Mozilla could technically make Firefox on Gecko on iOS/iPadOS for those markets.

The desktop Firefox on macOS uses Gecko like the Linux and Windows versions does.

The problem with trying to randomize a UA is that you are then making the UA more unique and the user easier to track. Mozilla has been making the Firefox UA more generic over the years as to why the build date been removed and the minor update version has not been shown since Fx 16.0.2? if I recall and Firefox on 32-bit Windows and Linux shows as 64-bit.

So reading all your three answers, I learned some browsers generate strange user agent strings, on purpose. Of course, I was not to test only it, also the behavior, but I was thinking the user agent notice could be a good hint to start with. It may not even be …

Will wait a bit before marking the topic as solved, in case some other people would like to say more.

Have a nice day