The page reports "Unknown code" ? Could you check for an explanation in parentheses (separated_by_underscore_characters). That may help identify the issue.

I noticed you have an extension named "Skip Cert Error 0.4.4.1" which may be modifying how Firefox (or Light ??) is reporting the problem. Can you get a clearer explanation of the reason the certificate is not trusted if you disable that extension?

When I visit the page, it does load. I get a gray warning triangle instead of a padlock because the site uses an RC4 cipher, which the past several versions of Firefox no longer consider to provide effective encryption.

Also, do you use any of these products which may filter your browsing using a "man in the middle" approach: Avast, AVG, BitDefender, ESET, Kapsersky, Microsoft Family Safety?

It shows An error occurred during a connection to forums.wildstar-online.com. Unknown code ___P 2

   The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
   Please contact the website owners to inform them of this problem.

I have uninstall Skip Cert Error 0.4.4.1 altogether, it is Firefox Light that I’m getting this error with, Standard Firefox will access the page, I was trying the Lite version to see how much difference there was in opening web pages and surfing the web, I noticed a pretty big difference but Lite won’t open the web page listed in the error message, as it’s a https: page.

How Do I get Lite to access this page or can't it be done in Lite?

Is there a Technical Detail section of the page with more information (hopefully)?

"Light" isn't a Mozilla product and I'm not aware that any volunteers here have ever tried it (I haven't). You could try this thread on another forum: http://forums.mozillazine.org/viewtopic.php?f=42&t=2764265

What do you mean a Technical Detail section, when I get the error page with it not accessing the https page, there is nothing else on the error page, just the message, no buttons nothing else just the error.

Okay, that is very different from Firefox. I'm not sure how to determine why you have this problem with that site without more to go on.

Does any more information appear in the Browser Console? You can try launching that using Ctrl+Shift+j or the Developer menu.

Is it the only site that gives you an untrusted connection error?

pressing Ctrl+Shift+J opens the error console, can I post the results that come up in that, if so how. So far yes it's just this site. Ok just retried getting to the page with the error console open and this is what came up, Timestamp: 17/09/2015 4:42:24 PM Error: An error occurred during a connection to forums.wildstar-online.com:443.

Unknown code ___P 2

Timestamp: 17/09/2015 4:45:00 PM Error: TypeError: this._recipeManager is null Source File: resource://gre/modules/LoginManagerParent.jsm Line: 86

Plus a whole lot of warnings, can't highlight all of them to post here.

Hmm, the second error is a couple minutes later than the first one, so I suspect it is not related.

I think this is related to something cut out to make "Light" and that product's support thread would be the next place to try.