My Android slablet died so I tried Hangouts in Firefox. It won't. This https://news.ycombinator.com/item?id=13763759
Whose fault it is seems to depend on whether you are a Mozilla or Google fanboi.
Google suggests Firefox ESR until they fix it, which isn't available from the standard Ubuntu repos. Raspberry Pi adoption of Chromium has made iPlayer work. Don't you just love open standards? It feels very like when they killed Hangouts competitors to me. First promote a new open standard so your main competitor commits then drag your feet and steal their customers. It could just be that Google doesn't have the resources.