Measure It is a Firefox plugin which will help you to measure the height and width of any element of a page. This tool is very useful for bloggers and web developers to see the exact dimension of any element or block on a web page.
Bloggers can take help of this tool to set the alignment of their web pages.
The addon is easy to install and use. Download the addon from the link at the end of the post, install and restart your Firefox browser.
On the bottom left you will see the ruler sign, click on it to enable it and start measuring any element of a webpage.
Download : Measure It Firefox plugin
Also read : How to minimize Firefox to System tray