lxpanel launch bar icons are broken

Question

I'm using lxpanel on my Ubuntu 14.04 laptop and facing this issue. Trouble is that the launchbar on the panel isn't displaying icons for some apps (or rather, the icons being displayed are generic white ones with a red cross-mark in between).

As you can see in the above image, the third icon for the geany app is problematic and isn't displayed and the same happens if I put firefox in the launchbar. However, all other icons seem to be displayed properly. Also, its noteworthy that issue with geany/firefox icons is only in the launchbar, in the taskbar and the main menu, it is displayed properly. I've also ensured that geany icons exist in the /usr/share/icons folder. I've also tried changing the gtk themes using lxappearance, but it didn't do any good. Can someone help me with this?

EDIT

When I right-click on the icons and go to the launch-bar settings, I can see a selector dialog like this from where I chose geany/firefox, but I see no way to change the icon:

Answer 1

I successfully changed the icon as follows (I'll use Iceweasel for my example):

1.Check your home folder for the LXpanel configuration at ~/.config/lxpanel/LXDE/panels/panel for a block specifying the launchbar:

Plugin {
  type=launchbar
  Config {
    Button {
      id=/usr/share/applications/lxterminal.desktop
    }
    Button {
      id=/usr/share/applications/iceweasel.desktop
    }
    Button {
      id=menu://applications/Internet/icedove.desktop
    }
  }
}

2.We found where the iceweasel.desktop config file is located. Now we look at said file /usr/share/applications/iceweasel.desktop for the Icon line:

grep Icon /usr/share/applications/iceweasel.desktop
Icon=icewesael

3.We change it to our new icon (as root) e.g. the icedove icon using a full path entry, so now the line reads:

Icon=/usr/share/icons/hicolor/128x128/apps/icedove.png

4.Restart the panel

lxpanelctl restart

Now you just need to figure out where your specific missing icon is.