There's a merged pull request on the void-packages repository

mobile-config-firefox: update to 3.1.0.
https://github.com/void-linux/void-packages/pull/40241

Description:
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Also change license to `MPL-2.0` as per https://gitlab.com/postmarketOS/mobile-config-firefox/-/commit/75c57aa3.

#### Testing the changes
- I tested the changes in this PR: **YES**

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