The Firebug entry point and also the only Firebug UI visible immediately after installation is s Firebug button (icon) placed at the right side of the navigation Firefox toolbar.
This button is called Firebug Start Button and its main purpose is to open Firebug UI by clicking on it (you can also use F12 key to open Firebug) but, the button does much more than just opening Firebug...
See all Firebug tips
Another purpose of the start button is indicating Firebug activation status. If Firebug is opened in your browser and collecting information about the current page (e.g. HTTP traffic) - the button is colored. If Firebug is deactivated and not representing any performance penalties - the button is grey.
|Firebug is activated|
|Firebug is deactivated|
There is also a tooltip associated with the button displaying detailed info about activation status.
Firebug is fully deactivated.
Firebug is activated on one page and panel Cookies is disabled.
If there are any errors on the page, the button indicates that by showing a badge with number of errors.
There is also a popup menu associated with the button
By default, the button indicates errors on the page and Firebug UI is located at the bottom. See detailed description of individual menu items on Firebug wiki.
Start button at the bottom
If you prefer to have the button at the bottom of the browser window (within Firefox add-on bar), use Firefox Customize Toolbar dialog.
Open the dialog through Toolbar Layout... menu.
As soon as the dialog is opened, you can drag the start button icon and drop it at the add-bar at the bottom of the browser window. That's it, don't forget to make sure the add-on bar is checked to be displayed (see the screenshot above).
If you have any tips how to improve this feature leave a comment, thanks!