Mac Mini OS X El Capitan cursor JUMPS in eBay text field!??

Hello, hoping someone can help me before I lose my mind. I work a lot on eBay and EVERY time I place my cursor in eBay's text box it jumps out and the whole page scrolls to the bottom, 5 or 6 steps beyond the text box. Ugh!!! Have a Mac mini running El Capitan. Please help.

Thanks!

Mary