I haven't used Mac s for decades, but I do run multiple profiles in Windows and Linux.

You probably are not opening the profile you expect. You are probably opening a single profile. Use the option in the troubleshooting page to open the profile and confirm which profile is in use.

• Profiles - Where Firefox stores your bookmarks, passwords and other user data#w_how-do-i-find-my-profile

Why does only the first script have an explicit full filename

... /MacOS/firefox-bin -P...

compared to the second

/MacOS/firefox -P...

Checking to see which profile each instance was using was the first and most obvious thing I did and each one is using its own profile.

As for the firefox-bin in the first code snippet, that was just me copying the wrong path when I composed my OP. Sorry, it should read just firefox.

Are you using Sync then ?

Or are you setting a bunch of tabs as the homepage ?

If you cloned a profile they will start off the same and that will include the set of open tabs from the file sessionstore.js however profiles are independent and so should have there own sessionstore and History once they have been used.

Did you confirm that Firefox is actually using the specified profile?

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

You can open the Browser Console (Firefox/Tools > Web Developer) and paste the JavaScript code in the command line and press the Enter key to run the code.

• toggle the devtools.chrome.enabled pref on the about:config page to true to enable the command line

var file = Components.classes["@mozilla.org/file/directory_service;1"].getService(Components.interfaces.nsIProperties).get("ProfD", Components.interfaces.nsIFile);
file.path;

As I said before, each instance is using its own unique profile, using either method to check.

Are you using Sync in both profiles to possibly sync the tabs?

Not using Sync.

I didn't know you COULD set a bunch of tabs as the homepage but I don't see how that would work.

You would think that each profile would use its own session store but that's not the case here as I pointed out in the OP. If I delete anything in one profile, it shows up again when I re-open the other one. I once had the problem of a portable FF app trashing my default profile of the installed version. That was long ago but it is another example of one profile interfering with another.

I do have Session Manager installed and have Show selected Session Manager session checked off. Maybe that's the problem as this add-on is quite buggy. I only use it because Suspend Tabs does not work without it. But AFAIK it doesn't store its sessions externally. Maybe it does but where?

Hmmm… when I look at the saved sessions, the latest one is about the time I created the new profile. It does not autosave like I believe TabMix Plus does. So that's probably it. I will change the default to Show my windows and tabs from last time and see if that works and report back.

OMG, I saved the session of profile 1 in Session Manager and it showed up in profile 1 clone and vice versa. This happens when both profiles are open or when one or the other is closed. I found out that SM stores all sessions in one single directory, and not in each profile as would be expected. Yet another obnoxious bug, IMO, found in SM. And I'm not the only one. I have lost many tabs and windows because of this damned add-on and now this… Does anyone know a good way to make Suspend Tab work when using TabMix Plus's own session manager without resorting to using the SM add-on?

<font size="6">The simple solution:</font>

I digress… Getting back to the original problem, it seems that changing default session behavior from <font color="#0000FF">Show selected Session Manager session</font> to <font color="#0000FF">Show my windows and tabs from last time</font> worked. Thanks to John99 for bringing up sessions. That led to the discovery of this seemingly innocuous setting. But now I absolutely must get rid of this pernicious Session Manager add-on. Someone PLEASE suggest an alternative that they know works.