>>> half the page is my browser home page and half is BT email page
Definitely weird!
Try resetting Firefox to its default settings:
Firstly, note down the names of any extensions that you've got installed (such as Adblock Plus) and wish to retain. To find them, click on the 'hamburger' icon (three horizontal lines, top right), then on 'Add-ons' and 'Extensions'.
Then click on 'Help' and 'Troubleshooting Information', followed by 'Refresh Firefox'. (If you can't see 'Help', at the top of your screen, right-click up there and put a tick next to 'Menu Bar'). Reinstall any extensions you need.