Duplicate application icons in Ubuntu dock upon launch

Solution 1:

You need to add a proper StartupWMClass line to the .desktop launcher corresponding to the application (refer to this). Follow these steps:

1. Open Files and go to your /usr/share/applications folder. Look for the "Nightly" file (i.e. the launcher for the application you want to fix) and copy it.
2. Paste the file in ~/.local/share/applications. It should look like a file with the name <filename>.desktop.
3. Right click on this .desktop file and open with Text Editor.
4. Launch "Nightly" (i.e. the application you want to fix) from "Activities".
5. Run xprop WM_CLASS in Terminal.
6. Place the cursor over the opened "Nightly" window. The cursor should turn into a crosshair already. Click. You should get a WM_CLASS string for "Nightly" in Terminal.

7. In the .desktop file opened in Text Editor add the following line

   StartupWMClass=OBTAINED-VALUE
   

   In place of OBTAINED-VALUE put a value you got from step 6 without any quotes.

8. Save the .desktop file.

Solution 2:

related to :

Kile icon buggy in left (launcher) bar (ubuntu 18.04)

On ubuntu 18.04

• open the file : org.kde.kile.desktop
• at : /usr/share/applications
• add this line at the end of file : StartupWMClass=kile
• press ALT+F2, r

It works for me

Solution 3:

Ubuntu 20.04 on Wayland

1. Press Alt + F2
2. Type "lg" and hit Enter (Looking Glass)
3. Click on the "Windows" tab.
4. You should see the titles of all your windows. Below each one you will find a wmclass property. Write down or copy the value you see.
5. Open up the .desktop config file corresponding to your application. It should be in the ~/.local/share/applications/ folder.
6. On a new line add wmclass=VALUE_FROM_ABOVE

In my case for Firefox it was "Firefox Developer Edition" and I had to add the line below to my .desktop file:

wmclass=Firefox Developer Edition