You can check the connection settings.

• Options/Preferences -> General -> Network: Connection -> Settings

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

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

See also:

• https://support.mozilla.org/en-US/kb/error-codes-secure-websites

SSL_ERROR_NO_CYPHER_OVERLAP Your server apparently doesn't offer any cipher suites necessary to establish a secure https connection that are supported in Firefox. You can check what kind of cipher suites Firefox can make use of by visiting; https://www.ssllabs.com/ssltest/viewMyClient.html

Firefox will just show the SSL_ERROR_NO_CYPHER_OVERLAP error when encountered any site using the RC4 cipher.

cor-el, FredMcD, Thanks for your replies. I tried what you suggested but it made no difference. It only occurs on one website [which ironically is that of my ISP] and I can work-around by using Chrome. I believe the problem lies at their end, but they don't seem interested in investigating. In view of this I will mark the problem as solved.

You can check the server.

• https://www.ssllabs.com/ssltest/

You can check your browser.

• https://www.ssllabs.com/ssltest/viewMyClient.html

Hi cor-el,

This is all a bit above my skill set but I tried running the tests you suggested.

The server test for www.plus.net produced Grade 'A'

The Browser test produced no vulnerabilities.

Attached are the two screen shots.

For me, if I check that website, I see these connection setting in "Tools -> Page Info -> Security".

• Connection Encrypted (TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, 256 bit keys, TLS 1.2)

This cypher shows in your second screenshot, so connecting to that website should work.

• https://www.plus.net/

You can 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

Boot the computer in Windows Safe Mode with network support to see if that has effect.

• https://www.bleepingcomputer.com/tuto.../how-to-start-windows-in-safe-mode/
• https://www.digitalcitizen.life/4-ways-boot-safe-mode-windows-10/

Hi cor-el, Sorry about the delay. I removed cert8 and renamed cert9. Re-started FF but the fault is still there. Restored the original cert9. cert8 has not been re-created. Is that relevant?

I don't understand your comments about starting Windows. My OS is Fedora Linux. Incidentally the 7Tutorials link produces "404 error"

Thanks

https://www.7tutorials.com redirects to https://www.digitalcitizen.life/

Did a search on the website: https://www.digitalcitizen.life/cse/?q=windows+safe&submit=

I fixed the not working link in my above reply. Thanks for reporting.

The cert8.db file was used in older Firefox versions, so Firefox won't recreate this file when deleted and I don't think that current releases still use it as a fallback, but it is best to be sure that leftover files won't cause issues.

You can try to update Firefox to the current 88.0.1 release.

• https://support.mozilla.org/en-US/kb/update-firefox-latest-version

Try the Firefox version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution.

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Hi cor-el,

I used the version from Mozilla server. Thanks for your help.