Since 2018 or so, iPad OS has supported multiple windows of the same application, but only if the app developer supports it. Safari, of course, supported this immediately. Google got around to implementing it pretty quickly on Chrome. Edge took years before they finally got there last year or maybe the year before.

Firefox, last time I checked (which was admittedly a few months ago) still did not support it. Plus, on their GitHub page, there was some talk about trying to implement it in a really dumb way, with each window sharing all the same tabs—completely defeating the point of the feature, in my opinion.

When wanting sync between my desktop (Windows), phone (Android), and tablet (iPad OS), I don't really care what renderer is used under the hood. I care what name brand is on the browser and what it's able to sync with. Firefox syncs with Firefox, even when Firefox is secretly Safari.