Ad Block Plus, Hobo. It's an add-on for Firefox. Once installed you just right click the offending ad and ban it.

Eccckkss,  PC's been running slower and slower,  so finally bothered to install  AdBlock plus and back to normal,  50% useage at all times with BM open,  just madness,  guess thats why it seems abit quite recently.

Never seen that before!!