Task Dacklet V0.20 Firofox & Thunderbirt Icon

I use Task Docklet V0.20 in RK Laucher.

I don't like the default icon of Firefox. So if I change the icon, then Firefox and Thunderbird show the same icon in Task docklet.

This is because both programs use the same ClassName ::MozillaUIWindowClass.

Does anybody found a solution to this old problem?

#537605