Unable to log in to site from Opera

[OUGHT]

I registered on this site in September. I like to use Opera, but I was forced to install Firefox specially for your site because of annoying bug.
When I try to log in from Opera, I receive the Error 300:
https://secure.wowinterface.com/login.php

The certificate is not known by its supposed issuer. It is not valid. In the worst case it may be used by criminals for fraudulent purposes. The website owner must immediately replace the certificate.

How can I fix this bug and deinstall the monstrous Firefox? =-)

[Dolby]

We use DigiCert which IE, Safari, Chrome & Firefox all have zero issues with. I loaded Opera (I didnt have it installed) and was able to access the page just fine (only a small warning if you click on the details info of the cert). Nothing stopped me from logging in via Opera using the link you provided.

I'm guessing Opera has issues with authenticating certs from the company DigiCert? I'll investigate this further tomorrow.

[OUGHT]

Thanks for the reply.
Looked into list of my Opera certificates: "DigiCert High Assurance EV Root CA" is present.

[Phanx]

I also use Opera, and have never had any issues logging into the site, or seen any warnings about it.

Do you have any security-related extensions installed?

Do you still have problems if you reset your Opera profile? (Exit Opera, then rename your "profile" directory.)

[OUGHT]

Resetting of profile didn't help me, but I found the solving of problem!
I used the anti-ad program AdGuard, and it blocked the login page. I just turned it off and all is working again!
Thanks for your help =-)

[Phanx]

If you want to use an extension to block ads, I'd recommend Ghostery. It's mainly aimed at blocking trackers and counters, but it also blocks ads, and has a very easy-to-use UI for allowing things on certain sites.