Firefox 39 does not handle spacing on a page with an embedded map properly since version 39. You'll see that map balloons do not function on mouseover unless you're the same distance away from it as the space on the page between the margins and the map. This doesn't affect full-screen maps, since there is no margin/border. I've filed a bug with Bugzilla, in case anyone wants to see the technical details: https://bugzilla.mozilla.org/show_bug.cgi?id=1182139
Hopefully, there will be a fix for this in a near-future release, but who knows... In the meantime I may need to convert all maps to full-screen maps or redesign tooltips - haven't decided yet.
So this means if you're a firefox user and haven't updgraded to 39, if you want maps to work here don't upgrade yet. This does not affect other browsers.