I think this is more a problem with developers working in Chrome and using Blink-specific features. I stopped having compatibility issues with my apps when I moved to Firefox years ago.
Some of it is Blink-specific, but some of it is silly Javascript stuff. How else do you explain a shopping cart final payment button not working.
I like development in Firefox too. When I was doing it intensively (just ~2 years ago), I found some of the CSS I was using behaved differently between Gecko, WebKit and Blink, though (and differently again in Android's pre-chrome browser), so I reconfirmed that I do need to test some things across all browsers. By differently, I don't mean prefixed browser-specific CSS (although there is that), I mean standardish things like table row height calculations showed up significantly differently, certain border highlights, and a number of WebKit rendering bugs that Gecko did not have. Key-event based text editing and wheel events are also significantly different, even more so when you include the common mobile browsers.
