Hi Michael, The top ad block is wrongly positioned in Firefox under OSX (I'm running v 53.03). In fact it is placed over some pretty important menu items. Screendump attached.
It's not actually blocking any menu items, but you are right that the Search button is missing from the top right corner when you are not logged in. I have reported it, and this will be fixed in the next update of the software we are using. Thanks!