That does not sound plausible to me. Typically, your own computer would be behind a router that is either doing NAT or has a firewall (probably the former). Any incoming traffic would be directed to the router without any chance of reaching your computer. Whatever you saw was either outgoing traffic or incoming traffic in response to connections initiated by your own computer.

Connection attempts from the FBI? Could you specify that a bit further?

There exists ~/.cache/mozilla (also ~/.cache/thunderbird), so I assume the cache is already separated?

I don’t actually care about the IP address, I am just curious if a website is accessed via IPv4 or IPv6.

Firefox (I am not going to repeat the obvious ones that have been mentioned numerous times):

• IPvFoo: Display IP address information for website
• tabdetach: I always juggle around my windows. Being able to detach, attach and merge tabs without using the mouse is really useful.
• Cookie AutoDelete: Removes cookies unless whitelisted

home assistant, freshrss (and a few related services such as rss-bridge), nitter and piped. I tried to host libregrammar, but ran out of memory.