Noticed an ad that had a pop up on the landing page...Is it because the ads might not be reviewed yet (geo - US)?
Yes, it will be because the ad has not been reviewed yet.
or is google allowing pop ups now?
Nope. No changes to the policy.
Are there different rules for IE/Firefox? I visited the site using both and IE didnt throw up a pop up (I know thats wierd - but I'm not dreaming).
No, there are not different rules per browser.
As an FYI, here is the Pop-up policy, quoting from the Editorial Guidelines:
No Pop-upsWe do not allow links to landing pages that generate pop-ups when users enter or leave your landing page. We consider a pop-up to be any window, regardless of content, that opens in addition to the original window.
AWA
