Did it ever? I normally find with most Google services I have to open up Chrome, and figured it's probably just them trying to get me to switch browsers.
This is also why Macs get scorchingly hot when using Hangouts on Chrome.
But yes, it's generally Google forcing their own products, just like what they're doing with YouTube, where you also get VP9 on Chrome and H.264 on Firefox.
Firefox is getting H.264 only because it doesn't support MSE for VP9.
A unified Mobile+Desktop solution is highly required so I can take conversations from one, continue them on another, and then bring them back to the original...which is why most of us switched to WhatsApp.