My Avast virus scanner prevented this and reported 2 issues: Win32-Malware-gen and MSIL:Crypt-HD [Trj].
I disabled Avast and downloaded the file. I sent it as a possible false alarm to Avast - but Avast confirmed in an e-mail the findings:
Kaspersky says: Trojan-Dropper.Win32.Agent.gen
VirusTotal says: 45 of 72 engines detected this file
Jotti’s Malware Scan says: 11 out of 15 scanners have reported malware.
What also makes me suspicious is the fact that the file palemoon-20.3-installer.exe from archive.org is smaller in size and has different properties than the one from archive.palemoon.org - but strangely it has the same files with the same contents in it when unzipping (with utility unpacked, not by running or self-unpacking!). Is there something else hidden in the file palemoon-20.3-installer.exe from archive.palemoon.org ?
I only downloaded this file palemoon-20.3-installer.exe - I can't say anything about the other archived files.
(Attached a few screenshots and page prints.)