Ubuntu – Firefox 82, create or edit shortcut

You can use your menu launcher creator (or right click the desktop and select new launcher, depending on what desktop you are on) to fashion two new firefox launchers. The command you need for each launcher is, for example:

firefox -Profile /home/mike/.mozilla/firefox/55divdmr.Mike2 -no-remote

This will launch firefox with that profile and make sure that it doesn't connect to any other running instance of firefox with the essential -no-remote switch.

If you wanted to do it manually, the desktop shortcut would look something like this; you could create it in a text-editor and name it firefox2.desktop:

[Desktop Entry]
Type=Application
Name=fox2
Comment=my second profile
Exec=firefox -Profile /home/mike/.mozilla/firefox/55divdmr.Mike2 -no-remote
Path=/home/mike
Icon=/my/icon/location
Terminal=false
StartupNotify=false

Something else I recommend is going to your firefox folder ( mine is /home/mike/.mozilla/firefox) and checking that the StartWithLastProfile setting in profiles.ini is false:

[General]
StartWithLastProfile=0

This is because it can get confusing if you are using different profiles and you start firefox as normal without using a special shortcut and it just loads the last profile used.

You can also get prompted each time for which profile to use by making sure 'don't ask at startup' is unchecked, which is in the firefox ProfileManager settings below. This setting is reached with

firefox -ProfileManager -no-remote

as noted in the question you referred to.

For more information on the command switches available for firefox see man firefox or the Ubuntu manpages online. Further support is available at mozilla.org.

Up until now, what you are doing is clicking the firefox dev edition's executable after you find it via nautilus (do not use sudo, it is not needed). But to launch an application in the usual way, you need a launcher file.

You can create a launcher file using the application menulibre. It is available in the Software Center.

Launch it, select "Add Launcher" and create a launcher for Firefox Dev Edition. For the "command" field, click on the folder icon, navigate to the file that you click to open the Firefox Developer Edition and select that.

Give it the name and icon that you want (leave the 'working directory' option empty), and you have a new application. You can add that to the Unity Launcher, and you can set it as default through System Settings>Details>Default Applications.

EDIT:

This error message means that you have another instance of Firefox running. You can't run Firefox if it is already running, so you get this error message. Make sure that you are not running Firefox (neither version) and try again. If you get the same error message, kill all Firefox instances with the command

killall firefox

and if that doesn't work, then kill all Firefox instances with the command

sudo killall firefox