Linux – Firefox mimetypes.rdf

It works now with firefox 29.0 on Linux:

To open a second firefox instance with a different profile:

firefox -P second -new-instance

To open a new tab in the second instance of firefox, which os already running:

firefox -P second -remote "openurl(http://example.com,new-tab)"

See Bug 716110 - split -new-instance flag out of existing -no-remote flag for additional hints (eg: post of Hayo).

As explained in the comments on this bug report, what is missing is a command that can be used for opening the first window and the second tab in the same way:

That could be done with a script along the lines of this (firefox-profile-instance):

#!/bin/bash

PROFILE="$1"
URL="$2"

if firefox -P "$PROFILE" -remote "ping()" >/dev/null 2>&1 ; then
    firefox -P "$PROFILE" -remote "openurl($URL,new-tab)"
else
    firefox -P "$PROFILE" -new-instance "$URL" &
fi

Now, while a firefox with the default profile is already running,
the first run of this starts a new browser with profile "second":

firefox-profile-instance second "http://example.com"

and running the same again opens a second tab in the same browser:

firefox-profile-instance second "http://example.com"

Well, I might as well answer to your question.

Try using the --class flag in firefox. If it matches the relative .desktop file, the various instances should be grouped correctly. For example, in your .desktop file:

Exec=firefox --class FirefoxDevel %u

It works for me for the same firefox executable, so as long as your versions support that flag, you should be good to go.