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I'm using Firefox 5 with some add-ons that require an external connection to a certain server (lastPass & Xmarks). I'm using the connection from my company, and every once in a while I get the following popup:

Secure connection failed.

This certificate in not trusted because the certificate issuer isn't trusted.

(Error code: sec_error_untrusted_issuer)

This also occurs using other versions of Firefox.

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Is your company connection using a proxy server? – TuxRug Jun 25 '11 at 6:04
No. Which is really weird. But I've to use a username & password to use it when I launch the browser. – Saifallah Jun 25 '11 at 6:13
That sounds like a "walled garden". In that case, there could still be a proxy server that isn't visible from your end. If that's the case, and there's an issue with the way the proxy handles SSL, it could cause this error. Try to visit https sites until you get an error stating that the certificate is not signed by a secure source, then check the issuer listed on that certificate. – TuxRug Jun 25 '11 at 20:17
And do what if I find the issuer? – Saifallah Jun 26 '11 at 5:02
See if the issuer is valid. You might see Verisign or another well-known certificate authority. If you see your company's name instead, or a servername that matches your company's naming practices (such as, then it could be a misconfigured SSL proxy somewhere on the network. – TuxRug Jun 26 '11 at 6:17

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