How are you opening each Firefox? Using batch file programs?

Make sure each is pointing to the correct FF version and its own profile.

For example (all on one line);

C:\PROGRA~1\MOZILL~1\firefox.exe -no-remote -new-instance -new-window -P Firefox_v_57

BTW, were you opening more than one version at the same time?

I'm opening them by the taskbar shortcut and by the Windows 10 start menu shortcut. And all shortcuts and their respective destinations and profiles are correct. This problem only occurs with Nigthly installed. I can open the developer and the normal edition simultaneously, but not the Nightly version. If I first open the normal version and then try to open the nightly, two normal version stays open, now if I open the nightly first and then try to open the normal version, two nightly instances are opened.

You cannot have two different Firefox instances running while using the same Profile as to why it seems you just get a second window opened instead.

Firefox since 2.0 has needed the -no-remote switch (Firefox 1.5 used MOZ_NO_REMOTE) to open the second Firefox instance with its own Profile. You can use either -P or -Profilemanager or start with a specific Profile.

Note do not use the -no-remote switch with the default Profile.

http://kb.mozillazine.org/Opening_a_new_instance_of_Firefox_with_another_profile

But that is precisely the problem. All versions have dedicated profiles, the shortcuts are all with the correct targets and I'm using the parameter P- "profile name" (without quotes) for each separate shortcut and profile. Not using -no-remote too.

Can't figure out what's happening.

Well if you do not use the -no-remote switch then you cannot run Firefox Release and Nightly at same time regardless if your shortcut has it so the version is to start with a different Profile. I think the Developers edition still has the features of using separate profile instance from when it was Aurora.

Please see http://kb.mozillazine.org/Opening_a_new_instance_of_Firefox_with_another_profile

When you have multiple versions of Firefox, only the default browser can be opened thru the taskbar icons.

Firefox is set up like this; When opened, it checks a file to see what the default (or last used) profile is, and opens it.

Whatever Firefox you try to use, it will load that profile.

In order to get what you want, you need to use batch programs with special switches.

Here is an example (on one line only);

C:\PROGRA~1\MOZILL~1\firefox.exe -no-remote -P Firefox_v_57

These are what I use. Note the profile switch at the end (-P) and the name after the Program Files.

C:\PROGRA~1\MOZILL~1\firefox.exe -no-remote -P Firefox_v_57

"C:\Program Files (x86)\Mozilla Firefox esr\firefox.exe" -no-remote -P FirefoxESR

"C:\Program Files (x86)\Mozilla Firefox 51\firefox.exe" -p default-1428275099518

https://developer.mozilla.org/en-US/docs/Mozilla/Command_Line_Options

Usage: C:\PROGRA~1\MOZILL~1\firefox.exe [ options ... ] [URL]
      where options include:
 
 -h or -help        Print this message.
 -v or -version     Print Firefox version.
 -P <profile>       Start with <profile>.
 -migration         Start with migration wizard.
 -ProfileManager    Start with ProfileManager.
 -no-remote         Do not accept or send remote commands; implies -new-instance.
 -new-instance      Open new instance, not a new window in running instance.
 -UILocale <locale> Start with <locale> resources as UI Locale.
 -safe-mode         Disables extensions and themes for this session.
 -console           Start Firefox with a debugging console.
 -jsconsole         Open the Error console.
 -browser           Open a browser window.
 -new-window  <url> Open <url> in a new window.
 -new-tab     <url> Open <url> in a new tab.
 -preferences       Open Options dialog.
 -search     <term> Search <term> with your default search engine.
 -setDefaultBrowser Set this app as the default browser.

Only the -no-remote is needed and not -new-window and -new-instance

The -new-window switch is not needed since you are not even using it to open a specific url in a new window and the -new-instance is not needed or even works on Windows.

The -new-instance is a old switch and not a new one in case you thought it was related to the new separate Firefox instances thing. It is said to not do anything on Windows anyways.

https://developer.mozilla.org/en-US/docs/Mozilla/Command_Line_Options#-new-instance Note: Not available for Windows, see bug 855899.

https://developer.mozilla.org/en-US/docs/Mozilla/Command_Line_Options#-new-window "Open URL in a new window. Firefox and SeaMonkey2.x only."

Thank you. I had been told those switches were needed.

Thanks, the -no-remote command resolved the issue.