Welcome to the forum Mieszko.
FYI: I created this article based on this thread.
https://www.os2world.com/wiki/index.php/How_to_Install_Firefox_on_Warp_4.52Since I didn't know exactly what was wrong with the ANPM installer on Warp 4.52 (Because it loops with the LIBPATH message). I intentionally put a "non recommended" setting on the PATH and LIBPATH so I can get the ANPM to complain and it will fix it. So, I understand that my settings are not the "good ones", but were the ones that broke ANPM loop on Warp 4.52 to let me install Firefox 45. Also remember that I haven't tried this on eCs.
Regards