That's annoying. Can you give a link to a site that has that design? In the past I've heard of Firefox jumping to a framed page -- many ads are displayed in a frame -- if they have a form field. However, this might not be related to that issue. Also, have you considered using an extension to block unwanted ads? For example: [https://addons.mozilla.org/firefox/addon/ublock-origin/]. As with any content-blocking technology, there may be pages that end up rendering incorrectly with an ad blocker, and when you spot that, you may need to make an exception for that page.