Map tiles not showing in firefox

I also have this issue when using sky/adaptive theme. I tried remove this code from adaptivetheme/css/at.base.css and sky/css/html-elements.css

img {
  max-width: 100%;
  height: auto;
}

Then it works. I think this is issue of adaptive theme.

Correct, the issue is with Adaptivetheme, in the latest dev versions of the theme I have included specific workaround for most mapping modules:

/* Override max-width 100% for map displays */
.gmap img,
.view-gmap img,
.openlayers-map img,
#getlocations_map_canvas img,
#locationmap_map img {
  max-width: none !important;
}