Want to know specific details about an image you are looking at? You can quickly find an image’s width and height with the Image Spider add-on for Firefox.
Now I can not see where this would be useful for your normal day to day Firefox users. I can see where it could serve as an important tool for web site designers. For any image on a website you can pull up details such as the width, height, natural width, natural height, and HTML elements such as the alt, title tag and border tags.
To use it, all you need to do is click on the new icon it places in the navigation toolbar.
In the options, you can define how the text box looks that delivers you all the image details, as well as the fonts for that text box and the border color that goes around a image after you have clicked the Image Spider icon.
Overall it is a simple extension for Firefox that does a great job at serving a simple purpose. You can download Image Spider yourself from the Firefox Add-ons web site.