What unique features does Firebug have that are not built-in to Firefox?

Question

I just cleaned my Firefox addons and wondered:

• Which features does Firebug have that make it unique?

• Which features are available in both Firebug and the Firefox Developer Tools?

Answer 1

Firefox's native developer tools have come a long way since this question was written. The differences have mainly reduced to the following points:

• Can't stop the script execution on DOM mutations, XHRs, or cookie changes.
• XPaths can't be copied.
• Missing an events side panel in the Inspector (though events are displayed within the DOM structure).
• Missing a DOM side panel in the Inspector.
• No live preview while editing HTML.
• Missing autocompletion for non-enumerable properties in the command line.
• Can't search within multiple files in Style Editor.
• No multi-line command line in the Web Console (though they have Scratchpad and a "smart-multi-line" command line)
• No toolbar buttons to toggle the tools or the Inspector.
• Can't search within responses of network requests.
• Missing autocompletion for several CSS properties.
• Missing several command line commands.
• Can't add cookies, just edit existing ones.
• No always-on mode and activation per domain (instead of per tab).

There are more things missing, which are tracked in a bug report filed for all the gaps between Firebug and the Firefox DevTools.

Firebug integration

Firebug is now built on top of the native developer tools. Since Firefox 48 there's also a Firebug theme that looks like the Firebug extension, letting you feel at home if you're used to Firebug. Once multi-process Firefox is enabled, pressing F12 or clicking the Firebug button opens the Firefox DevTools and with the Firebug theme.

There's also a migration guide explaining the differences between Firebug and the Firefox DevTools.