Firefox, the web developer’s debugging tool of choice
You will need to get several Firefox extensions:
View Source Chart
Creates a Colorful Chart of a Webpage’s Rendered Source Code
Easily view the source code of external js files.
Hypertext DOM Browser
Since IE never works quite the same as other browsers, you will find you need to debug in that environment also. Unfortunately it is not nearly as well set up for that as Firefox. If you have Microsoft Office, pop the install discs back in the drive and install the Microsoft Script Editor (use custom install and install it individually). Then you will need to go to
Tools->Internet Options…->Advanced->Disable Script Debugging (Internet Explorer)
Tools->Internet Options…->Advanced->Disable Script Debugging (Other)
If you are running IE 7 and above, there are Developer Toolbar addons that will help you debug CSS and layout issues.
Web development bookmarklets
Dreamweaver does a basic job of checking for errors in your HTML syntax. Use the “highlight invalid code” command under Code View options. You can also validate to various Web standards using the “check page” command in the File menu.