There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

Websites don't load - troubleshoot and fix error messages

http://kb.mozillazine.org/Error_loading_websites

What do the security warning codes mean

Bing search https://www.bing.com/search?q=PR_CONNECT_RESET_ERROR This simply means, that the peer or some middlebox in between (firewall) is terminating the connection.

Hi CWR, PR_CONNECT_RESET_ERROR indicates that the destination server or a server/router/middleman along the way sent a RST to Firefox to terminate the attempted connection. We sometimes can guess why that happened, but often a lot of guesses are needed.

Is this a new issue in Firefox 74 -- were you able to access this server on port 10000 in earlier versions of Firefox?

This is a new issue with Firefox 74.

Will your Firefox let you try non-secured access to the site:

http://192.168.0.253:10000/

If that doesn't immediately upgrade to HTTPS, do you get an error message for that address, too?

Could you try:

New Profile Test

This takes about 3 minutes, plus the time to test your problem site(s).

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

Click the "Create a New Profile" button, then click Next. Assign a name like Mar2020, ignore the option to relocate the profile folder, and click the Finish button.

After creating the profile, scroll down to it and click the Launch profile in new browser button.

Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.) Please ignore any tabs enticing you to connect to a Sync account or to activate extensions found on your system so we can get a clean test.

Do the problem site(s) work any better in the new profile?

When you are done with the experiment, you can close the extra window without affecting your regular Firefox profile. (Mar2020 will remain available for future testing.)

Note: if this test changed your default profile, use the Set as Default Profile button for your regular profile to set it back to normal.

jscher,

I created the url without the S and got the message that I needed to us the S

Then I created the Mar2020 new profile and tried the url and got the same error message and no Advanced to be able to add and exception.

CWR

CWR said

I created the url without the S and got the message that I needed to us the S

That was a message from the server? That helps: Firefox can find and contact the server!

So one possible explanation for this problem is that the server doesn't support the same secure connection parameters as Firefox. For example, it may only support certain encryption ciphers that are not included in Firefox but are included in Chrome. This tends to happen when server admins modify the list of permitted protocols and ciphers with the goal of removing insecure ones, but don't make sure that at least one cipher is supported by Firefox. I don't know how you can diagnose that with an internal server. (With a public server, a test page like https://www.ssllabs.com/ssltest/ can query the server and list out the supported ciphers and test connectivity of different browsers.)

jscher,

Since the earlier version of Firefox did not have the problem and there has been no changes made to the local server, it seems the problem must be with the newest version Firefox.

I just tried my laptop (also Win 10) that is using Firefox 72.0.2 over the same LAN to the same internal server and it is working fine.

CWR

CWR said

Since the earlier version of Firefox did not have the problem and there has been no changes made to the local server, it seems the problem must be with the newest version Firefox.

Thank you for checking that. To rule out corrupted program files, we generally would suggest this as the next step:

Clean Re-install

This takes about 5 minutes. It's not about your settings, it's about making sure the program files are clean (no inconsistent or alien code files). As described below, this process does not disturb your existing settings. It's not essential to uninstall Firefox, but you can if you like, saying No to any request about removing personal data.

If you want to make a backup first just in case, see: Back up and restore information in Firefox profiles

(A) Download a fresh installer for Firefox to a convenient location:

https://www.mozilla.org/firefox/all/

(B) Exit out of Firefox (if applicable).

If you have Microsoft Office installed locally, please change your default browser to Internet Explorer temporarily before the next step.

(C) Using File Explorer (hold down the Windows key and press E to launch it), right-click > rename the program folder as follows (you might have one or both):

C:\Program Files (x86)\Mozilla Firefox =to=> C:\Program Files (x86)\OldFirefox

C:\Program Files\Mozilla Firefox =to=> C:\Program Files\OldFirefox

(D) Run the installer you downloaded in step (A). It should automatically connect to your existing settings.

Any improvement at your next startup?

If the problem persists, the next step would be something more time-consuming that requires a high-bandwidth connection, a regression test between the last good release and the current 74.0 release:

https://mozilla.github.io/mozregression/

jscher,

I did the clean install, however I still get the same error message and no Advanced button to add an exception.

CWR

Is there any public server where you've had this problem? If not, I think you'll need to run the mozregression and see whether you can track down the patch that broke it.

Try to rename the cert9.db file (cert9OLD.db) and remove the previously used cert8.db file in the Firefox profile folder with Firefox closed to remove intermediate certificates and exceptions that Firefox has cached.

• https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean

If this has helped to solve the problem then you can remove the renamed cert9OLD.db file. Otherwise you can undo the rename and restore cert9.db.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

jscher,

Thanks for your help, but nothing has worked. At this point we will just use Chrome to go to https://192.168.0.253:10000/ and wait to see if the next version of Firefox will fix the problem for accessing a local server. CWR

A PR_CONNECT_RESET_ERROR is normally issued by the server that doesn't like the hello to negotiate the connection details.

Can you check logs on the server to see what is causing the server to close the connection ?

Did this work properly in older Firefox versions (i.e. can this be a regression) ?

You can try developer Firefox versions (Beta or Nightly) as a test to see if that works.

• https://www.mozilla.org/en-US/firefox/channel/desktop/

cor-el,

Thanks for your suggestions. Accessing the local server via https://192.168.0.253:10000/ did work with the previous version Firefox. For now, we will just use Chrome to access the local server and wait for the next released Firefox update. CWR

You can possibly do a test to see if you can find a regression range and file a bug report.

• https://mozilla.github.io/mozregression/

Does it has effect if you disable HTTP2 ?

• network.http.spdy.enabled.http2 = false

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

cor-el,

As you suggested, I tried changing network.http.spdy.enabled.http2 to false

But showed no improvement for the problem

CWR

cor-el and jscher,

Thanks again for your help. Yesterday the ability to view https://192.168.0.253:10000/ started working again! No updates have been done for Firefox, but possibly a Windows 10 update had something to effect the problem.

Stay Safe CWR