Internet Explorer Developer Toolbar:
The Internet Explorer Developer Toolbar provides several features for exploring and understanding Web pages.

This version of the Developer Toolbar is an updated version of Beta 1; it was updated on October 31, 2005. Several issues are resolved and some feedback has been incorporated.

— Element bounding box calculations are more accurate.
— Outlining of elements is now significantly faster.
— The image report no longer crashes.
— Installation no longer requires a reboot. (Beta 1 users will still be prompted to reboot because the current installer invokes the original uninstaller).
— The minimize and maximize buttons now refresh after the “Resize” command.
— The “Select element by click” bounding box is now more visible on pages with blue backgrounds.
— The attributes editor (middle pane) now has variable width fields (for example, you can type beyond the width of the box).
— Fixes for some pages that do not trigger OnDocumentComplete events.
— Fixed the continuity of using “element” rather than “tag” in the menus.
— The ruler is easier to use and to scroll.
— Enabling/disabling images no longer restarts Internet Explorer.
— The Resize menu now contains more resolutions.
— Editing a property is now much less likely to let keystrokes “leak” back to IE and navigate without the user expecting it.
— Trying to use the ruler while IE is in “folder mode” should no longer crash the browser.

I am sticking with Firefox and the Web Developer toolbar provided as an extension.