It used to be my favorite translator because it was so simple: 1click to translate, 1click to return to the original...
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Having neither found the solution nor understood your explanation, I had forbidden the Firefox update, because despite having configured not to update your extension, it was still being updated with the Firefox one. I just tried the FF update again yesterday, (from 119 to 121) and then miracle, the extension works again as before, same update, so I don't know who was guilty, the extension or Firefox. In any case, I'm happy to be able to continue using it.