I want to use some IDE which allows me to change the javaScript code on the fly and run it in browser. I don't think I can do this in Firebug.
Which IDE/software should I use for JavaScript development?
Yes you can do this in firebug console. Click on console and you can start typing. You can click on the bottom right red icon to expand the typing area.
The Sublime Web Inspector looks like it could do what your after.
It supports: