Firebug doesn't work with multi-process Firefox

Question

I miss Firebug. Everytime I try to run it I get this error:

Firebug doesn't support multiprocess Firefox (e10s). So you either need to disable e10s or upgrade to Firebug 3 alpha.

A button that reads Upgrade and Restart follows. It doesn't work.

Anyone knows how to solve this?

Answer 1

If the installation of Firebug 3 fails for you, you may need to go to about:config and set xpinstall.signatures.required to false. If the installation then still fails, you can download it manually from this page:

https://getfirebug.com/releases/firebug/3.0/

On a last resort you can also disable e10s by unchecking Firefox menu > Options > Enable multi-process Firefox/Firefox Developer Edition/Nightly.