Well, with the headaches that differences in HTML and CSS interpretation in browser engines already can cause, I would not look forward to having the same kind

Well, with the headaches that differences in HTML and CSS interpretation in browser engines already can cause, I would not look forward to having the same kind of problems with compiled languages. We could, of course, make the thing that compiles and executes the code a shared plugin, but then we would have reinvented ActiveX and Java applets.