Pixel Perfect https://addons.mozilla.org/en-US/firefox/addon/pixel-perfect/
Is not working any more on FF6 and seams that they will not update it, is there any existing add on or way to do the same thing this add on was doing?
About this Add-on
By toggling the composition on and off, the developer can visually see
how many pixels they are off in development.Pixel Perfect also has an opacity option so that you can view the HTML
below the composition. By being able to see both the composition and
the HTML you can now simultaneously use Firebug while Pixel Perfect is
still in action.
- Requires Firebug
For Google Chrome try "PerfectPixel by WellDoneCode" extension: https://chrome.google.com/webstore/detail/dkaagdgjmgdmbnecmcefdhjekcoceebi