You can have copyleft without virality; the Mozilla Public License 2.0 requires any modifications to a covered work to be released under the same license (copyl

You can have copyleft without virality; the Mozilla Public License 2.0 requires any modifications to a covered work to be released under the same license (copyleft), but does not extend this requirement to other code included in a combined work (virality). As I read the license, you could embed the Gecko browser engine in your proprietary e-reader software, and only your changes to the engine itself would have to be released as free software.