Firebug for Firefox:
Internet Developer Toolbar for IE:
- Explore and modify the document object model (DOM) of a Web page.
- Locate and select specific elements on a Web page through a variety of techniques.
- Selectively disable Internet Explorer settings.
- View HTML object class names, ID’s, and details such as link paths, tab index values, and access keys.
- Outline tables, table cells, images, or selected tags.
- Validate HTML, CSS, WAI, and RSS web feed links.
- Display image dimensions, file sizes, path information, and alternate (ALT) text.
- Immediately resize the browser window to a new resolution.
- Selectively clear the browser cache and saved cookies. Choose from all objects or those associated with a given domain.
- Display a fully featured design ruler to help accurately align and measure objects on your pages.
- Find the style rules used to set specific style values on an element.
- View the formatted and syntax colored source of HTML and CSS.