Setup: macOS Tahoe (26.4) and Firefox 149.0

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Behavior: Out of the blue this morning, every website I try to visit in Firefox returns "Looks like there’s a problem with this site". Every other browser works fine.

Things I've tried, that haven't fixed it: - Ruled Out DNS: Sites like 1.1.1.1 and my home router's IP return the same issue in Firefox, but also resolve in any other browser. - Firefox Safe Mode: no fix - Deleted All Settings, Reinstalled Fresh: - Removed the Firefox App, deleted:

       - ~/Library/Application\ Support/Firefox
       - ~/Library/Caches/Mozilla
       - ~/Library/Caches/Firefox

...and then downloaded and installed 149.0 fresh. - Refreshed Firefox (via [link] - about:preferences (toggled between FALSE and TRUE, testing each time) via this YouTube video

- network.dns.disableIPv6

- network.dns.disablePrefetch
- network.dns.disablePrefetchFromHTTPS
- network.dns.disable

....and in desperation, I checked my Mac for Malware (clean)

I'm at a complete loss: every other browser works, but Firefox is a 100% fail for all websites. Any thoughts?

I just started up my new MacBook Pro, M5 pro machine and Firefox will not work. Tahoe 26.3 is OS.

Dale Howard Jonesboro, GA

PS--Safari and DuckDuck Go browsers are working normally.

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

Every time I try to access Citbank to view my account I get a screen that says "Failed Connection". How can I stop this? This is "CITBANK" not Citibank. Thank you for your time.

HTTPS pages are no longer loading. Everything works fine in Microsoft Edge. I've reinstalled Firefox several times – the problem persists. Thank you very much for your help.

Almost every internet site that I go to using Firefox I get this message, "Hmm. We’re having trouble finding that site.". When I use Google Chrome or Microsoft Edge, I can get to the site? I really like using Firefox, but if it does not work?

My local network is 10.10.10.x and I can't log into my NAS, web server or another computer on the local network... Internet access is fine. Happens on Wi-Fi or Ethernet.

If I access the same web address using Safari or Chrome it works just fine and it used to work before the software update to the 147 build.

So what switch/setting got kicked over during the upgrade that I have to turn off?

These kind of issues really make me mad at the Firefox Dev team... and I'm a very long time user.