I had a ruler widget in opera which was quite handy when I wanted to measure the dimension of the web page contents. The measure becomes handy particularly when you are trying to get the idea of the size of tool box you are going to install to your page. Particularly, for my blog, I need it so that it will not be destroyed by the newest addition.
So, the story of opera with ruler was continued.
Every time, I wished for similar firefox extensions.
Today, I found a handy add on for firefox:
Try it out!
In my case the small icon on the left-bottom corner of the browser allows me to measure the dimension; just by dragging around the subject of interest!