Execute JS is Firefox/Thunderbird-Extension which provides an enhanced JavaScript-Console, where you can comfortably enter and execute arbitrary JavaScript-Code and modify functions.

These are the features of Execute JS:

• Execute arbitrary (multiline) JavaScript Code in every open window
• Evaluting the properties of an object
• Modifying functions on the fly i.e. you can search for functions, load and edit them and eventually save the modified function.
• Execute JS provides a persisent history of the executed code snippets as well as a basic code completion functionality
• Shortcut notations for frequent used expressions can be configured.

 

Read more..