Firefox stopped launching with Ventura 13.4

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Doesn't make much sense. Firefox is my default browser on seven Macs. Launches on all of them.

Install EtreCheck and post the report. Allow Full Disk Access.

https://etrecheck.com/

Use the Additional Text icon to paste in the report.

This might help shed some light on the problem:

https://support.mozilla.org/en-US/kb/firefox-wont-start-find-solutions

FWIW, Firefox 114.0.1 runs fine in Ventura 13.4 and later. Make sure you completely uninstall it before reinstalling. You really don't want to downgrade to Monterey.

Starting Firefox with the option key might work.

Did you try holding the option key and clicking on the Firefix icon in the Dock or dbl-clicking on the Firefox icon in the Applications folder?

Then try this, delete Firefox from the Applications folder and the Firefox folder in ~/Library/Application Support. Then download and reinstall.

Welcome.

It runs just fine for us on three Ventura Macs ... 114.0.1.

I suspect you have some other problem besides FF.

Thank you, this worked perfectly for me!