So, install Firefox 56, or 52 ESR, and never update it. Or run PaleMoon or one of its relatives, I suppose; that community's doing what it can to preserve archi

So, install Firefox 56, or 52 ESR, and never update it. Or run PaleMoon or one of its relatives, I suppose; that community's doing what it can to preserve archives of XUL-based extensions and API documentation.