The site could be temporarily unavailable or too busy. Try again in a few moments.
   If you are unable to load any pages, check your computer’s network connection.
   If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the web.

'''NOTE''': I have marked this as "Solved" because I figured out the problem described below, and I fixed it. See my following message here for a description of my solution. ''Original message starts here ...'' I'm using Firefox 144.0 under Debian Linux. I've used Firefox on this machine for years with no problem. Firefox can easily connect to literally thousands of web servers on the internet, both via HTTP and HTTPS. But now, I'm having an issue: I started running a web server on the same machine that Firefox is running on. This server only listens for non-HTTPS connections on port 80. I am not using any proxy server with Firefox. I can easily and directly connect to my local web server's pages from my local machine from Chrome, w3m, curl, and direct telnet connections to port 80 ... all of which are addressing the publicly accessible domain name for my local web server. However, However, Firefox refuses to connect to any URL's on my local machine, and it gives me the following explanation: '''''Unable to connect Firefox can’t establish a connection to the server at [ my server's domain name ]. The site could be temporarily unavailable or too busy. Try again in a few moments. If you are unable to load any pages, check your computer’s network connection. If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the web. ''''' In Firefox, I have all auto-forcing of HTTPS disabled by means of '''''Don’t enable HTTPS-Only Mode''''' turned on. I get the same error in Firefox whether I connect via a URL like "http://MYFULLDOMAINNAME" or a URL like "http://AAA.BBB.CCC.DDD", where "AAA.BBB.CCC.DDD" is my machine's publicly accessible static IP address and "MYFULLDOMAINNAME" is the long-standing, publicly accessible domain name for my machine ... both with and without a suffix of ":80" on the supplied URL. And again, all other browsers on my machine have no problem whatsoever connecting to my own local web server on this same local machine of mine using those same URL's. And all browsers (Firefox and otherwise) that are running on other machines all over the internet have no problem connecting to that same web server via the same URL's that I described above Also, I have no firewall rules on my machine which would block access to my own machine's port 80. What could be causing this error in Firefox, and what might I be able to do to fix it? Thank you very much in advance. '''UPDATE''': Just a bit more information. Looking at the web logs, I see that Firefox's request never even reaches my local web server. In other words, Firefox itself is not even trying to make a TCPIP port 80 connection to my local web server in the first place