Hi, i have the same problem. The plugin doesn't seem to work when the webgl is on. But when its off, it works. but the game lags as usual.
I can't really get either (tiledbackgroundfromurl, or loadurl) plugin to work very reliably. By disabling WebGL I can get loadurl to display an image on Firefox (though not on Chrome). The tiledbackgroundfromurl plugin makes use of a wait_for_textures call which I think is only useable in the object constructor, thus disabling the ability to load pictures at runtime. I do appreciate the hard work you put into this plugin though.