LGPL and MPL compatibility question

[Philippe Verdy]

Hugo Palma [mailto:hugo.m.palma at gmail.com] wrote:
> I know GPL and MPL are incompatible. But i'm just not sure if 
> that also means that LGPL and MPL are incompatible also.

If the GPL and MPL are incompatible, then the MPL is also incompatible with
the LGPL (because LGPL requires the compatibility with the GPL, as this is a
right granted by the LGPL to change it at any time to GPL, so that LGPL
libraries can be linked with GPL programs).

But to be really sure about this, what is the effective incompatibility
between MPL and GPL ? Does it mean that linking MPL programs with the GNU C
library is impossible? It seems that the LGPL was created exactly for the
purpose of allowing such linking with programs using other licences than the
GPL.

So I'd say that, as long as the LGPL library is linked with MPL, and remains
under LGPL, it does not violate the LGPL licence (but I don't know if the
LGPL rights or obligations violate some MPL terms): you can still extract
this LGPL code (which may have been modified for allowing correct
integration with MPL code), and then reuse it within another GPL program
(but you won't be able to reimport to a GPL program the MPL part of this
LGPL-MPL bundle).

Note that when linking a LGPL library with a proprietary program, this does
not make the whole program mandatorily covered also by the LGPL (there's no
"viral" behavior in the LGPL). And this should apply to the MPL as well as
other free or open-source licences.

Is it the "viral" behavior of the GPL that makes it incompatible with the
MPL? Which right or obligation of the MPL does the GPL remove or disallow?
Which right or obligation of the GPL does the MPL remove or disallow?