Standard development platform for the web browsers

Until recently I hadn't done much work for the web. I found the various inconsistencies about the way different browsers handle CSS and JavaScript quite annoying. I was wondering why hasn't anyone created something like the JVM for the browsers? I mean like a layer th开发者_JAVA技巧at runs on top of the browser which you can write code for and is consistent for all browsers? I know nothing about browsers so this question might be stupid.

Adobe Flash or Microsoft Silverlight