Firefox Developer Tools and Firebug
Here's a
Mozilla blog entry on current developments with the Firefox developer
tools. "
The tools have improved a lot lately: black-boxing lets you treat sources as system libraries that won’t distract your debugging flow. Source maps let you debug source generated by transpilers or minimizers. The inspector has paint flashing, a new font panel, and a greatly improved style inspector with tab completion and pseudo-elements. The network monitor helps you debug your network activity."