Board Thread:LotR Mod Technical Support/@comment-174.87.91.64-20190811000559/@comment-27219153-20190811141238

It seems that for a few people, Firefox is changing it to a .zip instead of a .jar which is (mostly) fine, mods will still run as a zip file. The only difference is that when the game starts up it checks for .jar core mods, and since it is a .zip it gets skipped. You can fix this by renaming it and changing the .zip to a .jar (make sure you have file extensions shown), or you could just download it from a different browser.