why does this website pop up

[southpaw17]

this website systemdoctor.com keeps taking over my firefox browser. It says it detects errors and wants to run a scan. I thought these problems were no existant on macs. I have had this error message come up at least 10 times in the past three weeks and I have to close firefox down and restart. How do i fix this?
thanks

 

[pianoman]

do you have the "block pop-up windows" boxed checked in Firefox prefs, under the Content tab?

 

[orangemacapple]

it's an advertisement. ignore it.
hit CTL CLICK and select block