So, it sounds like FF is sending something that's causing an RST to be emitted from either the website or (more likely) your appliance. Next step would be to pc

So, it sounds like FF is sending something that's causing an RST to be emitted from either the website or (more likely) your appliance. Next step would be to pcap/tcpdump a connection from both a working browser and FF, and see what the difference is. That kind of information is a lot more useful to FF devs than "something is happening that causes an RST from someone".