Last night I installed firefox-96.0-1.fc35 and I noticed that after a while it would not load any remote content either in new tabs or by reloading open ones. Websites that report on connectivity (e.g. gmail) display messages about having lost the connection. When this happens, I also get a GeckoMain process that seems stuck at 100-120% CPU and which has to be manually terminated after closing firefox. If I start firefox from a terminal, I get multiple repetitions of this message when the bug manifests itself:
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
could be a non-fedora issue
Closing this as NOTABUG, the actual issue was presumably caused by one of Mozilla's network service providers.
Waiting for an official announcement: