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can't find 9.15.13 anywhere

Это отзыв для предыдущей версии этого дополнения (0.9.15.13). 

You are right... but check the sandbox version... 0.9.15.13.
You must register here on addons.mozilla.org first, then it should show up when you select Show all versions. I did note that in the "long description."

Presently, it is marked as only to work with version 3.0 ~ 3.0.*... but you do satisfy that requirement.