ScreenShot 1.9.0 plugin for Mozilla browser is a free tool which helps you to capture and upload webpage screenshots to UploadScreenshot.com which offers free hosting service.
Using the Screenshot Addon, you can capture image of either visible area of the browser or the entire web page for uploading.
Screenshot adds a button to your browser which you can use to capture your preferred area of webpages.
Screenshots posted in UploadScreenshot.com are advertisement free. You can add ScreenShot plugin to your Firefox browser from here