How can I load an external JavaScript file using a bookmarklet? This would overcome the URL length limitations of IE and generally keep things cleaner.
Content security policy will prevent this from working in many sites now. For example, the code below won't work on Facebook.
Use a bookmarklet that creates a script tag which includes your external JS.
As a sample:
javascript:(function(){document.body.appendChild(document.createElement('script')).src='** your external file URL here **';})();