Yes, thanks! It's hard to describe, but this page nails it including the screenshots!

  Love your own

  There are two kinds of objects and functions - those that 
  are part of the standard DOM, and those that are from your 
  own JavaScript code. Firebug can tell the difference, and 
  shows you your own script-created objects and functions in 
  bold at the top of the list.

  To be even more discriminating, use the options menu to 
  completely hide different kinds of objects. For instance: 
  Show Own Properties Only hides derived properties from the 
  prototype chain, Show Enumerable Properties Only hides non-
  enumerable properties and Show Inline Event Handler shows 
  inline event handlers that are not associated with functions.

With "your own JS code" it means the JS libraries, the JS code of your website. Also any changes to DOM made by JS code is also highlighted in bold and different colors like green and red. Try it out yourself, you will see it's very useful undo you will ask yourself, why haven't I used it in the past.

I fear as it's now hard to impossible to try out Firebug with current Firefox, and the WebDevTools have long forgotten the past functionality of Firebug, we may never again get this valuable features back. :(

But to try it out yourself, either download FF48 portable and install an older Firebug revision (the last two Firebug revisions are "fake" meaning the basically remove Firebug, so use an older Firebug from 2015, you have to install it manually, or downgrade it)

Despite the downvotes by people who don't got it, it's a very valuable feature that made a Firebug so special and useful.

Please Mozilla devs, try it out, and you will get it in 1min how useful it is, and please add it to DevTools. (@Chrome devs: please also add it)