Microsoft contributed the code under "GPLv2 or later", despite samba being under GPLv3.

GPLv2 does not contain the explicit patent grant that are part of why GPLv3 was created. And I very much doubt the courts will consider "or later" to include the patent grant.

The code in question seems very peripheral (something about using Firefox for configuration), and have received zero comments on the developers list. I would be very surprised if Microsoft had any other motivation for the release, than to make the engineer who worked on it happy.

However, it is probably not an accident that they choose the version of the GPL without a patent grant.

It would be interesting to see the implicit patent grant in v2 (remember - you can't grant all the liberties required in the license without granting use - and the right to grant it further down the chain - of any patents embodied in the code) tested in court.

Also, unless I'm very wrong, the terms "GPLv2 or later" means you can use the software under v3 if you prefer to use it that way. The only way to block the explicit patent grant (but stay will the implicit one) would be to license it under plain v2.