Since Zotero 7 is based on Firefox 115, it's compatible with the Firefox 115 ESR Developer Tools.

Zotero beta builds come with the Firefox DevTools server preinstalled. Pass the -debugger flag on the command line to start it:

$ /Applications/Zotero.app/Contents/MacOS/zotero -ZoteroDebugText -jsconsole -debugger

If building Zotero from scratch, pass -rd to the build_and_run helper script to rebuild Zotero with the devtools server included and start Zotero with the server running.

In Firefox 115 ESR, you can then go to about:debugging, add localhost:6100 as a network location, and connect to your running Zotero instance. (If you haven't yet, you'll first need to enable the “Enable browser chrome and add-on debugging toolboxes” and “Enable remote debugging” options in the settings of Firefox's Web Developer Tools.)

You should use a separate Firefox profile for 115 ESR and disable automatic updates to prevent Firefox from being automatically updated to an incompatible version.