I often need to determine the size of a picture on a web site or to determine the size of a particular banner. Before using MeasureIT, Normally I just use my eye to determine the picture size, which is quite inaccurate.
Like me I would think that most blogger would also face this problem of trying to determine the size of a particular picture or area on a web site or even their own blog.
Firefox add-ons MeasureIT is a life saver for me, With this add-ons, I can now get the exact size of any elements on a web page, I can get the banner size, I can get the widget size and it saves so much of my time.
I highly recommended this add-ons if you often need to determine the dimension of an element on the web site.
Picture of MeasureIT 0.3.9 in action