1. When I set "NEVER REMEMBER HISTORY" Firefox create an initial INVALID INITIAL http request. GET /lipsum.html '''undefined''' <--------------------- HERE Host: myhost.com User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:120.0) Gecko/20100101 Firefox/120.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate, br DNT: 1 Sec-GPC: 1 Upgrade-Insecure-Requests: 1 Connection: keep-alive Sec-Fetch-Dest: document Sec-Fetch-Mode: navigate Sec-Fetch-Site: none Sec-Fetch-User: ?1 Pragma: no-cache Cache-Control: no-cache 3. This causes a NS_ERROR_NET_TIMEOUT_EXTERNAL 4. Firefox then immediately issues a 2nd HTTP Request, this time correctly. GET /lipsum.html '''HTTP/1.1''' <---------------------------- Host: myhost.com User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:120.0) Gecko/20100101 Firefox/120.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate DNT: 1 Sec-GPC: 1 Connection: keep-alive Upgrade-Insecure-Requests: 1 Pragma: no-cache Cache-Control: no-cache I have a video of the behavior and a simple HTML file to test with. I can't upload either.