Rated 3 out of 5 stars

This is a nice idea. However, there is an issue.
The size in the status bar is displaying the size of the Firefox WINDOW, but not the size of the actual VIEWABLE AREA. For example things like the status bar, menu bar, bookmarks bar, tabs bar and side bars all take up room that makes the website actually SMALLER then the size given. In my case, I have my tabs on the left hand side of the screen going up and down, and this takes up more space in the window.
So what am I getting at? There should be TWO modes to Firesizer. One will calculate the screen size by how big the WINDOW is, and the other mode would calculate it by how big the actual viewable area is inside the window. For me, these two numbers would differ in several hundred pixels.
Thanks for the consideration...
Regards,
Scott

This review is for a previous version of the add-on (1.0). 

This functionality is by design, and is specifically stated in the description. It makes no sense to me to have the HTML area resize when no user is ever using only an HTML area. If you are a developer and creating web sites and using the HTML area size as your target, you are doing it wrong, since no real user would ever be seeing your site like that. There are some other extensions that resize to the HTML area and not the whole window.