hello alexandra123, a possible solution depends on different factors:

• what is the error code shown under technical details on the error page?

in case the error code equals sec_error_unknown_issuer, please attempt to add an exception on the bottom of the error page & inspect the certificate (see the screenshot attached for instructions):

• which issuer information does the certificate contain?

thank you!

"This Connection is Untrusted" error message appears - What to do

'address' uses an invalid security certificate The certificate is not trusted because no issuer chain was provided. (Error code: sec_error_unknown_issuer)

I should not have to Add Exception for every single site I want to visit! It's ridiculous. Especially that I cannot add Hotmail at all. Plus, the Mozilla website does not work in Mozilla. How is that possible? I am getting this weir wiev with blue writing, like the website is broken or safe mode or something.

hello, you should NOT ADD ANY EXCEPTIONS! please just attempt it once to find out who is issuing the failing certificates like displayed in the screenshot, but don't add exceptions for real. those error messages are showing up for a reason - something is intercepting your secure network connections & it's important to find out what it is (it can generally be misconfigured anti-virus programs or also malware in other cases)...

Thank you. But this does not solve my problem. I ran Kaspersky full scan for hours, and it did not find anything. So my problem remains and I do not have a clue what to do.

we still need to diagnose what's going on before we're able to solve it - please report back in the forum who issued the failing certificates.

Thank you.

Organisational unit: Created by http://www.fiddler2.com Serial number 5A:13:2D:7C:39:B5:F7:8C:45:22:84:8A:64:3F:45:7B

Is that it? It obviously looks like virus, but Kaspersky did not detect it.

ok thanks!. yes, unfortunately the fiddler2.com issuer in certificates might be a sign of unwanted software present on your pc that is intercepting secure network traffic. please go into the system control panel and uninstall programs like BrowserSafeguard, BrowserSafe, SafeGuard or other software that sounds suspicious and didn't get installed by you intentionally. _{reference: https://support.mozilla.org/en-US/questions/982532#answer-520145}

afterwards, run a full scan of your system with different other security tools like the free version of malwarebytes & adwcleaner which are specialised in detecting adware and browser hijackers.

Troubleshoot Firefox issues caused by malware

Thank you, that is very useful! I will use one of these programs, but after scanning, can they delete the files for free? Normally they ask for money.

yes, those products are reputable and fully functional without the need to pay anything. please run a scan with both of them - you could uninstall them again, after they have done their job...

OMG it worked!!! Thanks for advice. The first one didn't do much and I scanned twice. But adwcleaner did it within 5 minutes! And he detected rocket tab that I was trying t get rid of for weeks!