hello, can you try to replicate this behaviour when you launch firefox in safe mode once? if not, maybe an addon is causing troubles here... [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]]

Yes, it is replicated when launched in 'safe mode', i.e. the ads still appear.

another thing you can try is to [[Reset Firefox – easily fix most problems|reset firefox]]. in case there are still adverts shown in places where they aren't supposed to be afterwards, it sounds like an issue with malware on the system. please run a full scan of your pc with the security software already in place and different tools like the [http://www.malwarebytes.org/products/malwarebytes_free free version of malwarebytes], [http://www.microsoft.com/security/scanner/default.aspx microsoft safety scanner] or [http://www.kaspersky.com/security-scan kaspersky security scan]. [[Troubleshoot Firefox issues caused by malware]]

The reset fixed the problem. Thanks very much.