Bug 455508 - Revert experimental change.

modules/libpref/src/init/all.js

@@ -2668,7 +2668,7 @@ pref("toolkit.zoomManager.zoomValues", ".3,.5,.67,.8,.9,1,1.1,1.2,1.33,1.5,1.7,2
 
 // Image cache prefs
 // The maximum size, in bytes, of the decoded images we cache
-pref("image.cache.size", 10485760);
+pref("image.cache.size", 5242880);
 // A weight, from 0-1000, to place on time when comparing to size.
 // Size is given a weight of 1000 - timeweight.
 pref("image.cache.timeweight", 500);