when a pop up appears its contents immediately go transparent, eg when typing in a web address, matches are displayed in a box that immediately goes transparent - how do I stop this?

I don't really understand what you mean here. Could you submit a screenshot of what you're seeing? Thanks!

see image When I start to type a URL in the address bar, a drop down appears with matches to what I am typing. As soon as it appears, the outline of the box remains but its contents go white, so you cant see and therefore select anything that is displayed (or not in this case!) in the pop up.