Hi, in what way did you install 2 Firefox's ? As there is a lack of compatibility if installed to the same place and Profiles are in the same place. Or do you just have 2 Profiles ?

This is likely about having multiple (two) Mac user accounts that are both active at the same time.

Does it has any effect if you open a new window or do you really need to quit and restart Firefox?

Yes it is about two Mac user accounts that are both active at the same time.

I can open a new window but still can't do anything. I really need to quit and restart Firefox. And this is the only app that has this problem.

I think this is common on all apps. I use Win10 and if I just open Browser on different account it will close the other Browser. Since both are running from the same folder it must close one or the other to run in the current active accounts. I know, I had other software tell me to close the other before it would run.

Like I said this is the only app that has this problem. I would hope this is not common on all apps in Windows or Linux. macOS easily handles multiple users simultaneously running with proper memory allocation and app management for multiple instances of the same app.

This is obviously a Firefox problem, not an OS problem.

If that was the case we hear more about it but that isn't here. If your saying is true we hear from other mac user mentioning back here for others to know more.

I found that a few things worked but after a several seconds delay.

More importantly I found that if I closed the window and opened a new one, everything worked just fine.

As for "If that was the case we hear more about it ..." I doubt if many people would even encounter my situation where two user accounts are open and a user is going back and forth between them. Generally different people use different user accounts with only one open at a time.

And what I said is TRUE!!!