Firebug Lite for IE7
In cases where I need to debug dom or javascript on older browsers, I’ve used Firebug Lite, which can be installed (in theory) on any browser with just a bookmarklet. However I found that neither of the latest versions 1.3 and 1.4 of Firebug Lite work in Internet Explorer 7, but version 1.2 does work.
Also, the following bookmarklet can be used to roll your own, or just drag this link to your bookmark bar: 🚀.
javascript:var%20firebug=document.createElement('script');firebug.setAttribute('src','http://getfirebug.com/releases/lite/1.2/firebug-lite-compressed.js');document.body.appendChild(firebug);(function(){if(window.firebug.version){firebug.init();}else{setTimeout(arguments.callee);}})();void(firebug);