hello mikeoev, first please make sure that the date, time & timezone are set correctly on your system. if this doesn't solve the issue (or it is already set properly), 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 (but don't do it for real) and inspect the certificate (see the screenshot attached for instructions):

• which issuer information does the certificate contain?

please report back with those pieces of information. thank you!

this is what I get from my yahoo email...This Connection is Untrusted

You have asked Firefox to connect securely to login.yahoo.com, but we can't confirm that your connection is secure.

Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do?

If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue.

This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox only connect to it securely. As a result, it is not possible to add an exception for this certificate.

login.yahoo.com uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. (Error code: sec_error_unknown_issuer)

thanks, can you try a workaround to inspect the failing certificate? first enter chrome://pippki/content/exceptionDialog.xul into the address-bar and on the interface that opens enter "https://login.yahoo.com" into the location server field. click on get certificate & view and see what issuer information it contains (see screenshot) and report back with that in the forum.

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History") or via the about:permissions page.

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, cookies, passwords, cache, history, and exceptions, so be cautious and if you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of the involved files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.