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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

I've been using Thunderbird on a Windows machine for years. I now have an iMac and recently downloaded Thunderbird to start transitioning over. When I try to set up an existing Email address, the configuration is found in the Mozilla ISP database. After I enter the password though (mobile.charter.net), I get an error stating "Unable to log in at server. Probably wrong configuration, username or password". The password is correct and works on the Thunderbird version on the Windows machine. I have multiple Email addresses and I get the same error on all with verified correct passwords. Any help to correctly install would be greatly appreciated!

When I open the Thunderbird desktop app we receive this popup error message:

"Unable to establish TLS connection to POP3 server. The server may be down or may be incorrectly configured. Please verify the correct configuration in the Server Settings for your mail server in the Account Settings window and try again."

I have not found any configuration under the account settings to help with this, but if anyone has any suggestions to walk me through this to establish a connection again that would be most appreciated.

Additionally, when I try to send an email I receive the message: "Login to server smtp.cybermesa.com with username centinela failed."

After closing the error message box I received another error message: "Sending of the message failed. The message could not be sent because the connection to Outgoing server (SMTP) smtp.cybermesa.com timed out. Try again."

Is our issue then with Cybermesa and not Thunderbird? Or Is something wrong with Thunderbird due to our initial error message we received? Any suggestions is much appreciated.

I am using 140 ESR version on linux with Cloudflare's DNS over HTTPS and with DOH active for some reason resolving a domain like d3oklwo3y1bx83.cloudfront.net will resolve to local host IP 127.0.0.1.

I am using firefox about:networking#dnslookuptool to test resolution of the domain d3oklwo3y1bx83.cloudfront.net Both with DOH on and off the resolution remains local host. I tried another browser on the same workstation and I was able to receive a resolution of 13.225.193.203 13.225.193.133 13.225.193.64 13.225.193.58 Why is firefox ESR not able to resolve that domain? What are causes ?

Is is firefox dnslookuptool results.

The connection was reset

The connection to the server was reset while the page was loading.

   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.

What can I do to resolve this problem.....Problem loading page

ich kann von Anfang Dezember an nicht mehr auf mein Arcor Mail zugreifen äh der sagt der Server ist nicht erreichbar habe schon alles versucht hier mit Windows 7 ist der PC ich habe zwei PCs mit Windows 7 und beide gehen nicht nur am Windows 10 habe ich wieder hinbekommen aber Windows 7 Minuten ich bin schon am verzweifeln oder geht das nicht mehr in Windows

I am setting up a new computer with Linux Mint and Thunderbird. I got my primary comcast.net account added in and working but when trying to add another account I get the following:

Unable to connect

The connection was refused when attempting to contact localhost.

   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 Thunderbird is permitted to access the web.

Since the first account works, I assume there is no problem with network connection, firewalls, or proxy settings. I have confirmed spellings of username and password. Any ideas?

This just started 4 or 5 days ago ( 2026.1.23 ish). I did not update TB nor make any changes to the account in question (that I'm aware of). The errors show up every few minutes, with a 'beep' sound and notification pop-up showing up each time - is very annoying.

I was running v145 when it started. I saw there was an update to 147 and installed that; same issue. I restarted TB into Troubleshooting mode and am still getting the error.

This is running on MacOS 15.7.3. Hardware is MacMini (2024) with Apple M4 chip.

Generally I still seem able to received & send emails.

I opened Activity Manager and Error Console. Error console doesn't seem to have much (using 'Multiprocess', with Errors, Warnings, Logs, Debug enabled). Activity manager shows things such as:

<my account name>

   Connection to server outlook.office365.com was interrupted.    09:49
   Failed to connect to server outlook.office365.com.    09:52
   Authentication failure while connecting to server outlook.office365.com.    09:58
   Authentication failure while connecting to server outlook.office365.com.    10:03
   Connection to server outlook.office365.com was interrupted.    10:10
   Connection to server outlook.office365.com was interrupted.    10:14
   Connection to server outlook.office365.com was interrupted.    10:20

There was an error or log entry that I was able to find a few days ago that made me think it was Calendar related, but now I'm not finding that message.

I just installed NORD VPN, and I can no longer send any emails in Thunderbird. Receiving is just fine. Gmail works fine. The addresses in Thunderbird are all Spectrum charter.net addresses. I have spent over 5 hours trying to get his working, seeking help from every possible source that I could think of. The spectrum addresses can send and receive just fine when logging into spectrum. This is probably a pretty common association, that is Nord VPN and Thunderbird. And with the big black Friday sales there should be plenty more people with the same situation. If you can give me any ideas about a solution, I would be most grateful. Thank you Bill Lowe

Quand l'envoie une PJ avec un compte qui a smtp.free.fr, j'ai le blocage "L’envoi du message a échoué. Le message n’a pas pu être envoyé car la connexion au serveur sortant (SMTP) smtp.free.fr a expiré. Veuillez essayer à nouveau." Si je l'envoie avec un compte qui a smtp.sfr.fr, je n'ai pas de problème ! Je suis en Thunferbird 146.0.1 (64 bits) sur Windows 10. Merci de votre aide.

For over a year, my browser occasionally loses connectivity. It may work for 3 hours or 3 days, but inevitably new tabs will stop working and then slowly the others will stop as well. When this happens, none of my other browsers are impacted. They work fine. It is only Firefox. The only solution is to close everything and lose all my work.

Once I do that and restart Firefox, I receive an error message telling me I am using an older version of Firefox that is not compatible with my profile. The only solution that brings me back to the best starting place is to re-install Firefox.

My company IT spent 3 days trying to find the problem and couldn't. I have uninstalled and reinstalled so many times. All extensions are turned off, as are the two add-ons. I have been using Firefox for over a decade and prefer it to all other browsers, but I need to find a solution or I am going to have to move on. Help!!!

The connection has timed out

The server at eofficepwd.kerala.gov.in is taking too long to respond.

   * itemThe 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.

the msg returned

Hmm. We’re having trouble finding that site.

We can’t connect to the server at marvelsearch.com.

If you entered the right address, you can:

   Try again later
   Check your network connection
   Check that Firefox Developer Edition has permission to access the web (you might be connected but behind a firewall)

i am using a local dnsserver and firefox is connected to it. is this the reason? if so how can i disable this? other firefox features are working beautifully.

Why did retrieving messages suddenly stop. It was working yesterday and I made no changes to anything. I can send successfully. I am using Shaw/Rogers Pop server.

Why does "test connection to server" fail?

I used to use the basic version of Thunderbird on a daily basis, but after a while it became buggy and didn't work properly. I've been using Thunderbird beta for 3 months now. I had to take a break from work because I need to add multiple Outlook emails to Thunderbird online for one thing. I've been doing the same thing for three days now, adding emails to receive notifications about shipments ready for pickup.

After adding 2 to 5 accounts, a message pops up saying that my data is incorrect, but it is 100% correct. When I try again, an exchange error pops up, and when I check through my regular browser, I can log in and check my mailbox normally, but it does not connect to Thunderbird beta or Thunderbird daily.

And so, for 3 days, I added 2 to 5 accounts correctly, and then finally, no account wants to be added. I checked that Thunderbird has no limit, I saw about 300 accounts per day, but the accounts I'm doing are a ridiculous limit and I have some problem with the application, and before I used it the same way I do now and had no problems. Thunderbird Daily works just as badly, no works from 2 to 5 accounts, then an error pops up. What's going on with this???!?!

Hello,

My father has a random issue with one of his email accounts. Context: Windows 11, TB 146.0.1. In TB, 5 mail accounts are configured, all IMAP, on 4 different providers.

All accounts work perfectly except the first one, which is also the default account. This account and the second account are both on my father's Internet provider. The configurations of both accounts seem identical (I checked more than once), except obviously for the name and password. On the first account (which is unfortunately the one my father uses most), connexion is often refused, and TB then asks to retry or enter a new password. Retry and reentering the password fail to solve the issue. When the connection to the first account fails, the second account (for the same provider) always works. Some time later (usually at least several days later), the first account will work again, without any obvious reason.

I tried exiting TB as well as clearing the cache, rebooting the computer, scanning for viruses, with no result.

I'd rather avoid re-creating the account in TB as this would change the order of the accounts, and my father (94 years old) might have difficulties to adapt to the change, but is someone can tell me how to recreate the account without changing the order, I am ready to try it.

I have a log of what happens when using only the "bad" account, and one for the good account from the same provider, but I don't know how to share them here. While creating the logs, I checked that if I set the second account as default (the first account having the issue before as well as after this), it still manages to connect. But of course, maybe the second account would have also had a connection issue later...

Does someone have any explanation, or ideas about how to solve this issue?