Fennec outbound license is Apache 2.0. Hence, any new code, designs, and efforts contributed back to the project must comply to the outbound license.
There are the licenses forbidden from integrating into the project due to inbound licensing incompatibilities:
- Proprietary licenses
- GPL Version 2 license and similar Copyleft licenses
- Missing license
- Unknown licenses
You must always understand where do you get the idea/codes before you apply into the project itself.