Catch the time dimension !
Chartlet is a Firefox extension that periodically checks places on the Web, extract and stores numerical values. On demand, you can display the history of those values in nice charts.
Not only you can capture a value directly displayed on a page, like a temperature or a stock quote, but you can also extract the rank of an item in a list, or the number of occurrences of an expression in one or several pages.
Of course, you have a total control of what is retrieved by your browser and how often extractions happen.
Each extraction configuration is controlled by a chartlet. You can install and run as many chartlets as you want.
Using Chartlet is easy. Once the extension is installed, just click on a chartlet link from http://www.chartlet.net and you will have the option to install it on your browser with simple customisation. You can also create your own chartlets to extract values from wherever on the Web.