The pop ups are super annoying. But, you can turn them off.

Go to ff.net's main page, and move your cursor over "help" which is right under the "sign up" option in the top toolbar. A number of options will drop down when you roll your cursor over 'help,' and one of them is 'ad blocker.' Click that and it will take you to another page that asks you to 'click here' in order to block pop ups for a day. Click it, and then you're done. :) If you use the back button to get back to where you were, you'll need to refresh the page, but then you should be pop up free for a whole day.

Hope that helps! :)