Since it underpins so much of the modern browser ecosystem it becomes a primary target for webapps to work.
As such, if you want to be sure a website will work you use chrome.
Since chrome has such a market share, developers feel justified testing primarily for chrome.
Self-fulfilling cycle.
This isn't the 90's anymore where browsers behave wildly differently for the same page content. If you're not using absolute, bleeding age web APIs, Firefox and Chrome work identically. In my experience, there are exactly 3 types of websites that work differently between Firefox and Chrome: The Toy Hobby Experiments (who are just demoing some bleeding-edge API feature), The Monopoly-Bootlicking Liars (who reject my request based on UserAgent string alone, and when I spoof a Chrome UA the site works perfectly), and the Evil Monopolist Themselves (a few of Google's own sites run notably slower on Firefox, most notably Google Cloud Console).
Weird how vmware console and my bank don’t support firefox.
Oh, and Microsoft Teams for a super long time (haven’t checked in a little while).
Theres dozens of examples tbh.
Teams has worked on Firefox (on Windows at least, haven't tried on Linux) since at least the beginning of the pandemic.
Can't speak to the other two. What does the console start screaming about when you try?