The MPLv2 was specifically designed to be compatible with as many FOSS licenses as possible. It was not possible to make it compatible with GPLv2 however, because the GPLv2 is incompatible with any license that has explicit patent clauses (which I would consider to be a historic accident and a serious issue with GPLv2).
That issue was resolved with a specific section in the MPLv2 that allows licensing the code under (L)GPLv2+/AGPLv3+.
1.12. “Secondary License”
means either the GNU General Public License, Version 2.0, the GNU Lesser General Public License, Version 2.1, the GNU Affero General Public License, Version 3.0, or any later versions of those licenses.
The MPLv1.0/v1.1 allows automatically upgrading to any later version of the MPL, in section "6.2. Effect of New Versions. ". Therefore (IANAL etc.) any code published under MPL is compatible with GPLv2+.
That issue was resolved with a specific section in the MPLv2 that allows licensing the code under (L)GPLv2+/AGPLv3+.
The MPLv1.0/v1.1 allows automatically upgrading to any later version of the MPL, in section "6.2. Effect of New Versions. ". Therefore (IANAL etc.) any code published under MPL is compatible with GPLv2+.