This add-on will show you what JavaScript gets to run on a web page, even if it is obfuscated and generated on the fly. Simply open JavaScript Deobfuscator from the Tools menu and watch the scripts being compiled/executed.

The code displayed comes straight from the JavaScript engine of the browser. Whenever the JavaScript engine compiles or executes a script it is added to the corresponding list. The rules at the bottom of the Deobfuscator window define which scripts should show up. By default, browser's own scripts and extensions are excluded but the filters can be adjusted to show those as well. The JavaScript engine reformats the source code so that it is easier to read - there are also some artifacts however like some functions appearing twice.

Note: When the JavaScript Deobfuscator window is open all code executes much slower. Only open it when you actually need it.