Firefox Download Tool is freeware that can download many versions of Firefox in any language, 32-bit or 64-bit.
Firefox Download Tool is a portable app and easy to use. By default, it begins with the latest version and the default language in 32-bit. The bottom bar tells you what version you are currently looking at.
This means that you'll want to check the box for Other to see what versions are available and be sure to choose 32-bit or 64-bit. A status bar shows you the status of your download, and it also can show you the MD5, SHA1, and SHA256 information. It also includes a Virus Total link for scanning.
However, while Firefox Download Tool claims to download all versions, this is simply not true; not even close. It only goes back about ten release and even then, misses some of those leading me to believe this was hand-coded and not pulling the information from Firefox releases channel.
For example, at the time we reviewed this, 52.0.2 was the latest version, and this tool only goes back to the 43.x versions. In the 43.x releases 43.0.4, 43.0.3, 43.0.2, and 43.0.1 are available but there's no link to 43.0.
We love that Firefox Download Tool is free and portable, but you might be better off browsing all Firefox releases here, especially if you want a really old version.