Mozilla pops-up a tab with nothing on it?

[grazhopper]

Alright this has been happening for about a month. I will be looking on the internet, and out of nowhere, a new tab pops up that has nothing on it. The address of the site is on the actual tab. If someone tells me how to take a screenshot or something ill post one.

 

[Cromewell]

Do a spyware scan, you've probably got some adware detecting that you are surfing and it's trying to pop an ad up.