My GPX-Viewer had a problem in Firefox: For some visitors OpenStreeMap maps would be displayed with pink tiles and not the real map tiles. This is a known problem which occurs when the server being used to load the tiles does not send an appriopriate HTTP header for CORS.
I don’t have control over these servers – but fortunately there is a workaround in the OpenLayers library which I use, so the “pink tile” problem with OpenStreetMap maps in Firefox should not occur any longer.
The solution was to add the option crossOriginKeyword: null
when adding the map layers:
map.addLayer(new OpenLayers.Layer.OSM.Mapnik( "OpenStreetMap Mapnik", { tileOptions : { crossOriginKeyword: null } } ) );