Firefox won't open on iMac

If you hold Option key while launching the app, it will start into Troubleshoot Mode with a lot of things skipped. Does that one work or also fails?

Holding the OPTION key while attempting to launch Firefox does not appear to do anything. The dock icon still bounces once, but no other sign of life. Is there an event log I can check for errors?

And after bouncing it does exit, i.e. there's no "dot" under the icon it's running, even without any window etc.?

The quickest would be checking if running the binary via Terminal prints any errors. If you search in Spotlight for "Terminal" system app to open it, you can try launching Firefox from there. For most default setups the location/command to run would be:

   /Applications/Firefox.app/Contents/MacOS/firefox -safe-mode

but feel free to adjust to your location (if you type just a few letters, case–sensitive, and "Tab", it would autocomplete the path segments for you to avoid typos etc.)

Documentation: wiki.mozilla.org/Firefox/CommandLineOptions#macOS

I checked to see my last reply ... with the screen shot showing the "Killed: 9" response to my attempts to start Firefox from the terminal. I see the attached screen shot, but not my text. So I will try again, in case it never got posted.

This is equally puzzling as the conventional launch silent termination. This usually means the app is not trusted, or it's corrupted to the point of causing memory issues and such so it's terminated.

Could you try downloading the separate nightly.mozilla.org and see what happens if you launch that one? (The difference also is that it comes with its separate fresh profile, so it might work around other, potentially profile–related issues.)

Also, if that one starts up, it's possible it would be able submit your previous crash reports in case the damage was so severe to even prevent collecting & submitting them.

The Nightly launched and I was able to skip around to various URLs. I haven't tried to sign in or create/synch a profile. Didn't want to mess it up. Just what do I need to do from here (e.g. submit prior crash reports, if any)?

Running the "-ProfileManager" command did the trick. I did not create a new profile, but Firefox 153.0.1 popped right up, even using my previously configured URL. I removed the Nightly version. Thanks for your help ... and patience! P.S. I tried posting this reply 3 times now, but have not seen it show up. 3rd time's the charm?  ;-)

Lovely! Once you're done with the cleanups there will also be a leftover "default–nightly" profile folder that you won't need going forwards — the easiest is probably going to about:profiles in your release and removing that –nightly one from there (should still be visible), the profile manager should prune all the relevant records for you that way so you don't have to tinker with it manually.

Yeah about that. I "quit" Firefox and attempted to restart. All I can get to now is the "Choose a Profile" box (1st attachment). No matter whether I pick the original, or create Profile 1 and pick it, Firefox does not launch. And now that I un-checked the "Choose a profile on Firefox opens", I get nothing but 1 bounce out of the icon in the dock - just like my original problem. So no chance to issue the "about:profile" command there.

So I launched Nightly, did the "about:profile" and see 3 profiles (attachment 2). Two of the 3 say they can't be deleted. Not sure if one of them belongs to the original Firefox or not. Either way, not sure how to proceed to cleanly ditch Nightly, and re-establish Firefox.

And given that the weekend has started, please understand there is no priority to resolving my issue. I have Safari and Chrome to fall back on as needed.

If it were this simple, it would have just started previously, right?;)

Okay for now please keep all the profiles — they are luckily marked correctly as necessary so none can be deleted in error… and since you might need the separate Nightly to actually set things straight, please do keep it for now (and feel free to use it in the meantime as well — it would be helpful to see it works without any further hangs or crashes between restarts etc.)

This looks like something is afoot with defaults, as in, which profile to launch with.

So if you try the terminal launch to profile manager again:

maybe this time let's create a new profile from here, and set it to launch next time?

To at least get to the point the dock icon starts with "any" profile correctly, before trying next steps.