Often when using Firefox 73.0.1 in Xubuntu 18.04 to browse a web forum about a retrocomputing hobby,* I see 30-minute periods when all connections to that website time out but connections to other websites and non-web Internet resources continue to work. Checking through the website "Down for Everyone or Just Me?" during such an outage shows that the outage affects only me, as does asking other users on a Discord server and an IRC channel related to the website's subject matter.
Comparison of a traceroute to the server during both working and outage periods shows that my packet stops just as it leaves Cogent's network. I have evidence (from a source that I cannot disclose publicly) that the first IPv4 address after the packet leaves Cogent is the IP address of a firewall that sees a bunch of SYNs (the first packet in a TCP outgoing connection) from my IP address and blocks my home Internet connection's IP address as a measure against denial of service (DoS).
I managed to capture getting blocked using Wireshark on my laptop's WLAN interface. (It has no wired Ethernet interface.) The packet log shows 19 SYN packets from my laptop for the first page view and 17 for the second, each with a different ephemeral port, most of which it immediately closes with RST. This burst of 36 SYNs in 4 seconds appears consistent with what my source told me.
So I want to limit Firefox's rate of connection to that site and only that site. Turning off these settings in
about:config did not help:
Others have suggested reducing
network.http.max-persistent-connections-per-server, but I hesitate to reduce this because it would slow access to all other websites as well. Is there a way to keep Firefox from being too eager to connect to websites under a particular domain name while behaving as usual for other websites?
* I hesitate to name the website for fear of appearing to unduly promote it.