If you click the close X on that adv then they shouldn't appear the next time you visit this Google page.

Note that this is stored in local storage (aka super cookie) and not in a normal cookie, so if local storage is disabled or otherwise not working properly then this adv will keep appearing.

You can check if DOM Storage is enabled.

• http://kb.mozillazine.org/dom.storage.enabled

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Also see peter7187's reply on this question for an Adblock Plus rule that will block the popup.

No this didn't work. I went into about:config and toggled "dom.storage.enabled" to false and that didn't work. Then I went into Safe Mode and went into Tools, Add-ons, extentsions and disabled the latest Google update and that didn't work either. I can't see why I had to go into Safe Mode though. I looked through all the add-ons and extensions and there didn't seem to be anything likely to cause this problem except the Google update.

Isn't that the opposite of what cor-el recommended?

"Note that this is stored in local storage (aka super cookie) and not in a normal cookie, so if local storage is disabled or otherwise not working properly then this adv will keep appearing. "

You should leave DOM storage enabled (dom.storage.enabled = true)