The debian-alternatives system is better than the KDE one, but there shouldn´t exist 2 systems.
So:
1. Thunderbird should use the browser set by the alternatives system
2. Threre should be a littel GUI to set options for that system
3. The KDE settings to set a web browser and email Program (and whatever is managed by debian-alternatives) should be removed, instead the debian-alternatives settings should be used.
I don´t know in how far the ubuntu team modifies KDE but this should be possible and is IMHO the most user-friendly and best solution
What I think of the correct solution:
The debian-alternatives system is better than the KDE one, but there shouldn´t exist 2 systems.
So:
1. Thunderbird should use the browser set by the alternatives system alternatives) should be removed, instead the debian-alternatives settings should be used.
2. Threre should be a littel GUI to set options for that system
3. The KDE settings to set a web browser and email Program (and whatever is managed by debian-
I don´t know in how far the ubuntu team modifies KDE but this should be possible and is IMHO the most user-friendly and best solution