Measure it - adds a ruler to FF for pixel pushing: https://addons.mozilla.org/en-US/firefox/addon/539
Web Developer Toolbar - adds a whole bunch of inspector type stuff https://addons.mozilla.org/en-US/firefox/addon/60
Color Picker - Lets you get the color of a pixel by clicking on it https://addons.mozilla.org/en-US/firefox/addon/271
IE also has similar tools: http://en.wikipedia.org/wiki/Microsoft_Script_Debugger http://www.microsoft.com/downloadS/details.aspx?familyid=E59...