All of the releases of Firefox are available via FTP at this URL:

https://ftp.mozilla.org/pub/firefox/releases/

The resulting page is entitled: Index of /pub/firefox/releases/

Downloading Firefox via this method will not do any preliminary checking of your environment or compatibility, so that responsibility is yours.

In case you are not familiar with FTP, it is a very old and widely used file transfer protocol that in modern browsers, including Firefox, acts very similar to traditional http/https protocols. Just put the URL in the address bar and hit enter.

The page itself is very detailed - so be precise when you are looking for what to download. Scroll down (it is a very long list) to the entry: Dir 65.0.1/ and click on it. On the next page, click on either the Dir win32/ or the Dir win32/ link - which ever matches your laptop and Windows version (this Microsoft link will show you how to tell: https://support.microsoft.com/en-us/help/827218/how-to-determine-whether-a-computer-is-running-a-32-bit-version-or-64).

The next screen (and list) lets you pick your desired language. For example, I pick the Dir en-US/ for US English.

Finally, the last page will display the executable file: Firefox Setup 65.0.1.exe. Click on that and it should ask where you want to save the file. Pick a place, where you can easily find it later, and let it download. Then go to the location where you saved the file and click on the .exe file...and Firefox should install.

Two points: First, as it executes, the setup routine may do some checking - so if it fails to install, it may mean you picked the wrong file to download. Second, if you selected the win32/ version, you will also see the option to download the Firefox installer instead of Firefox itself. That is an online install (which may be where you were failing before). It is really only useful if you can't download the full Firefox code because of its size (about 41 megabytes).

Hope this helps.

PPort said

All of the releases of Firefox are available via FTP at this URL: https://ftp.mozilla.org/pub/firefox/releases/ In case you are not familiar with FTP, it is a very old and widely used file transfer protocol that in modern browsers, including Firefox, acts very similar to traditional http/https protocols. Just put the URL in the address bar and hit enter.

https://ftp.mozilla.org/ is not FTP as ftp://ftp.mozilla.org was FTP.

Mozilla discontinued the ftp:// protocol on their servers back on August 5, 2015. The ftp://ftp.mozilla.org has not worked since whether in a web browser or in a FTP client.

https://web.archive.org/web/20161006070213/https://blog.mozilla.org/it/2015/07/27/product-delivery-migration-what-is-changing-when-its-changing-and-the-impacts/

After 8/5/15, ftp protocol support for ftp.mozilla.org will be completely disabled and downloads can only be accessed through http/https.