I actually do suspect it's intentional, but have no way to really prove it.
My guess is RAM management/garbage collection going on in the background that needs to whitelist a few things or have some additional fancy stuff going on to not allow for memory leaks but allow for 2 hour phone calls and searchable PDFs after they've been open for some time (and possibly with a 10+ tabs open).
Definitely file a bug. I would imagine both these issues are known about and have a similar root cause.
I love Firefox otherwise.
https://news.ycombinator.com/item?id=18697824
https://arstechnica.com/gadgets/2018/12/the-web-now-belongs-...
Google intends to kill Hangouts by the end of the year anyway:
https://www.theverge.com/2019/1/22/18193303/google-hangouts-...
I don't have any proof for this, but I think everything I've seen about Google's Invoice was also meant to kill the open email standards by convincing everyone that the proprietary "AI-enhanced" features of Invoice were worth it over interoperability with other email providers.
Thank goodness that app failed. They're still trying to do it through Gmail now, but it's going to be a much slower process and hopefully people will have enough time to catch on to them before it's too late.
Google is becoming a monopoly in the classical "evil company" sense - a monopoly that's no different than any other monopoly in the past, and that will try to exploit the users and kill competition in the same way others have done it before. More people should start to seriously consider this before going more "all-in" with Google than they already have.
That sums it up nicely.