Firebug makes changes immediately and gives constant feedback to the user. All editors in Firebug support autocomplete.
HTML and CSS
The HTML and CSS tools allow for the inspection and editing of HTML and CSS elements on a web page. Later versions of Firebug allow users to see live changes to the CSS. Visualization of CSS elements is shown while inspecting HTML elements. The Firebug layout tab is used to display and manipulate CSS property values. Furthermore, users can click on any visible HTML elements on a web page to access its CSS property values.
Many extensions have been made to enhance Firebug. Since Firebug is open source, users can contribute their own extensions to the Firebug community.
FlashFirebug is a paid Firebug extension that helps Flash and Flex developers debug Adobe SWF files on the web. FlashFirebug was developed by O-Minds and is licensed under the GPLv3.
In February 2012, O-Minds purchased the code to FlashBug, a competing Firefox extension. Flashbug had extensive capabilities to parse AMF and Shared Objects objects and partially decompile Adobe SWF files directly in the browser. Soon after the purchase, O-Minds integrated key features of FlashBug into FlashFirebug and retired Flashbug from the AMO repository.
Currently the extension displays textual Output from trace() commands within the Adobe SWF movie, a Display Tree with the hierarchy of display objects and their properties, viewers for AMF and Shared Objects, and a tool to modify the 3D transformation of any display object on the stage.