Is it okay to rely solely on websockets these days? I was always impressed by pusher.com's commitment to a variety of fallback protocols (and there are three blog posts about it, see https://blog.pusher.com/how-we-built-pusher20-part-1/)
It's not a question of browser support, it's a question of infrastructure support. When I was using them years ago, there were a lot of networks which blocked them.
Not affiliated with anyone here, but I think the answer is yes.