Opened the URL you posted and didn't get any pop-ups. Check if you have Block pop-up windows enabled in Settings for web content, pop-ups, fonts, and languages. You might want to review is my Firefox problem a result of malware too. Hope this helps.

The problem aren't pop-ups. This site and other sites like this (about Science, Muscle-building, Technology, Cars etc.) are suddenly opening in new tabs (and not in new window, like pop-ups) during browsing. I've tried to use other browsers too, but as Firefox is set to be my default browser, these sites are opening Firefox.

I've just found an add-on here: https://addons.mozilla.org/en-US/firefox/addon/3145/

I had no problem for now (at least in the last half-an-hour), so I hope this will help.

Do a malware check with a few malware scan programs.
You need to use all programs because each detects different malware.
Make sure that you update each program to get the latest version of the database.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
• http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page

See also "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked and What to do when searches take you to the wrong search website