I was going to make a joke about giving Firebug a look but (TIL) Firefox's Devtools actually subsumed Firebug a few years back. That's pretty cool and a nice note for that project to end on.
They make it sound nice, but the last release of Firebug was after that page says they were unified, and only about half a year before Firefox Quantum removed XUL, which would have killed Firebug anyway. I was still using Firebug because its console was still better than the built-in devtools.
https://getfirebug.com