CloudMade/Leaflet — pull request #1171 by dreamfall (2012-11-23 15:32:14+00:00)
Title: Fix error in initializing map in hidden iframe in Firefox

Firefox `window.matchMedia("(min-resolution:144dpi)")` returns null if it is called on hidden iframe. So we need to check if ` window.matchMedia("")` is not null before calling another method on it.