How to fix the thunderbird no icon problem in LXDE Desktop and panel icons.
When I installed Thunderbird on VL light B5 using gslapt there was no icon on the .desktop file. I installed , reinstalled thunderbird. Even a new distro install. The problem is the lxde icon located in /usr/share/pixmaps does not match the one called for in the .desktop config file. The program icons are actually determined from .desktop files located in /usr/share/applications. To correct the missing icon, in /usr/share/applications right click on the space where the icon should be. Open the file in a text editor then modify the icon= string to show the same icon that is in /usr/share/pixmaps. The icon should then appear in the menu and anywhere there is a . desktop file. I have not encountered any other missing icons, but this would be the first thing I'd check if I did.
PPS: you must be root to do this