Think that the add-on manager in Firefox looks a little busy? Maybe there is a little too much wasted space there for your liking? No matter what the reason is, I have an extension for you to try out that will give you a much more minimalistic add-on manager interface.
That add-on in question you need to install is called, Cleanest Addon Manager. Here is a little more about the extension from the developer:
This tiny restartless addon cleans up wasted space from the Addon Manager in Firefox/Thunderbird without compromising any functionality. Very useful if you have a long list of addons or a small sized screen and hate to scroll every time you want to access an addon.
Want to shrink down your own add-on manager and see more than just a few items without having to scroll down? You can pick up the Cleanest Addon Manager from the Firefox Add-ons website.