hello, this sounds like a problem possibly caused by malware on your pc. please go to firefox > addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc). also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there and do a full scan of your system with the security software that you have in place and different other tool like the free version of malwarebytes & adwcleaner.

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

One of 2: Malicious plugins in Firefox (disable them control panel) and run Adwcleaner : [www.bleepingcomputer.com/download/adwcleaner/] Or Malware Run TDSS Killer http://support.kaspersky.com/faq/?qid=208283363 and Hitman Pro or Spyhunter

many thanks to all who answered. I think I've solved it now. Hope so any way! It seemed to be 'Madpersons' answer of Add ons and extensions. There were about 6 items i removed and it seems to have done the trick! many thanks! Ron