Firefox Beta instances are shown under Firefox Stable in the dock. How do we associate the Beta instance with the Beta launcher?

Question

The directory ~/.local/share/applications/ includes three files associating with different versions of Firefox, namely

---

1. Firefox - firefox.desktop

[Desktop Entry]
Encoding=UTF-8
Version=1.0
Type=Application
Name=Firefox
Icon=/opt/firefox/firefox/browser/chrome/icons/default/default128.png
Exec=/opt/firefox/firefox/firefox
StartupNotify=false
StartupWMClass=Firefox
OnlyShowIn=GNOME;Unity;
X-UnityGenerated=true

2. Firefox Beta - firefox-beta.desktop

[Desktop Entry]
Encoding=UTF-8
Version=1.0
Type=Application
Name=Firefox Beta
Icon=/opt/firefox/firefox-beta/browser/chrome/icons/default/default128.png
Exec=/opt/firefox/firefox-beta/firefox
StartupNotify=false
StartupWMClass=Firefox Beta
OnlyShowIn=GNOME;Unity;
X-UnityGenerated=true

3. Firefox Developer Edition - firefox-dev.desktop

[Desktop Entry]
Encoding=UTF-8
Version=1.0
Type=Application
Name=Firefox Developer Edition
Icon=/opt/firefox/firefox-dev/browser/chrome/icons/default/default128.png
Exec=/opt/firefox/firefox-dev/firefox
StartupNotify=false
StartupWMClass=Firefox Developer Edition
OnlyShowIn=GNOME;Unity;
X-UnityGenerated=true

---

The problem:

At the moment, all Firefox Beta instances are associated with the Firefox Stable launcher icon.

The expectation:

All Firefox Beta instances must be associated with the Firefox Beta launch icon.

Answer 1

Simply using the StartupWMClass=Firefox Beta line is not enough, you need to assign a valid and distinct WM Class to the launcher accordingly first.

Change the

Exec=/opt/firefox/firefox-beta/firefox

line to

Exec=/opt/firefox/firefox-beta/firefox --class FirefoxBeta

and then change the

StartupWMClass=Firefox Beta

line to

StartupWMClass=FirefoxBeta

Do the same with the other one.

(adapted from this answer)