javascript the most misunderstood language

when you get started with javascript ,when you open some programs in browser let us say (mozilla firefox) some of them will work in mozilla firefox and some others are not.
Why is it so?
one of the reason is due to its rendering engine
and one more thing you should know something about the history of javascript.
Intially javascript called as livescript was developed by Netscape navigator.At that time java was popular ,so they named it as javascript.Microsoft saw this programming language and they reengineered it and come up with their own programming language called jscript which is similar to javascript but differs in certain features.so in order to standardize their model netscape navigator went into Ecma (european computer manufacturers association ) and it is called as ECMAscript which is nothing but javascript.