Ya know, my initial reaction to this was pretty negative. As a developer, I don't like the idea of losing access to a more powerful technique in favor of a less powerful one. If I want to write an add-on, I <i>want</i> XPCOM / XUL, etc., at least as an option.<p>However, giving it more thought, I think this might actually be a Good Thing in the long-run. OK, it's a stretch, but hear me out... I've been a vocal opponent of this whole idea of making the browser a poor man's operating system for a while. I want a Web where browsers are really good at, well, <i>browsing</i> hypermedia, and other applications handle "application stuff". So maybe, in a roundabout fashion, making it a little bit harder to extend the browser even further, will encourage people to shift back to a model of handing off some kinds of requests to an entirely different app, rather than trying to shoe-horn the kitchen sink, bathtub, 3d printer, milling machine, jumper cables, semiautomatic pistol, bandsaw, swimming pool, and clown suit all into the browser.<p>Or maybe not. Hey, a guy can wish, right?