ECMAScript is the standard version of what is generally known as JavaScript.
The name JavaScript is mainly historical (though almost everyone uses it instead of the more technically correct name) and was invented by Netscape Corp. for their new browser scripting language in the old days (when men were real men, compilers were real compilers and small furry creatures from Alpha Centauri were sci/fi authors with too much to drink). Netscape donated their work to ECMA (a standards body) and promptly started adding all kinds of Netscape specific stuff to their implementation leading to the mess of browserspecific JavaScript versions in use today.
Most any browser supports ECMAScript, if you stick to it you have effectively a common platform for your code.
It's similar to the story of ANSI C where compiler manufacturers often added their own non-standard "enhancements" which break compiler compatibility.