Firebug is on of the famous extension for inspecting web pages in firefox. Now it is possible to use firebug in any browser using Firebug lite. Firebug lite is the small version of Firebug with limited features and usage, but has the full capability.
In order to do this, just save a bookmarklet and use it whenever needed.
Bookmarklet
Drag the link to your bookmarks toolbar. That’s all. The script which is loaded for the usage is
Source: Firebug official site