installation file corrupt

If the compact installer or the other means do not work, you can either grab alternative way like a .MSI here: https://www.firefox.com/download/all/desktop-release/

or if you use Microsoft Store get your Firefox installed from there as an alternative: https://www.firefox.com/download/all/desktop-release/win-store/

Thanks for the tip, but it didn't work.

I downloaded the .MSI file for 64 bit and got the same error: File is corrupt See attached.

If I were you I'd get the system scanned for any viruses or malicious software — as this sounds like something's trying to compromise the installer immediately — and the checksums then don't match so it doesn't proceed.

(Or conversely it can be a AV scanner poking its nose into any downloaded exe/installer and corrupting the file in the process, dunno. Or you're using a downloader that can't handle these?)

You can get any version directly from archive.mozilla.org/pub/firefox/releases/ — the installers are also accompanied by checksums that you can verify after downloading — in case you're not getting the same on your end.

all good thoughts but not solving the problem. A full scan shows nothing. The Firefox installer (downloaded 5 times) says it's 18.5.0.0. Nothing like that shows up in the archive.

Hi,

While that's super weird, have you already tried installing Firefox from Microsoft Store? In that case, Windows manages the installation, which may work around whatever issue you face.