Did reCAPTCHA change? Unless Google has published a note on what versions of Firefox work with it, I don't know how you're going to figure that out.

The last version of Firefox that ran on Windows Vista was Firefox 52.9.0esr. If you would like the installer for the U.S. English version, you can find it here:

http://archive.mozilla.org/pub/firefox/releases/52.9.0esr/win32/en-US/

If you prefer a different language, click the .. link to move up to the parent folder and you can find it there.

Current Firefox releases require Windows 7 and later. Users on Windows XP and Vista have been moved to the Firefox ESR version.

• https://blog.mozilla.org/futurereleases/2017/10/04/firefox-support-for-windows-xp-and-vista/

• https://support.mozilla.org/en-US/kb/end-support-windows-xp-and-vista
• https://support.mozilla.org/en-US/kb/your-hardware-no-longer-supported

Besides updating to Windows 7, 8 (8.1), 10, you could also consider using a light 32-bit Linux distro like Lubuntu, Xubuntu among some other distros that still support the ancient 32-bit CPU's.

As either will be the only way you can use current Firefox versions.

At least use 52.9.0 esr as suggested as it was Released on June 26, 2018 and much more up to date with security and stability fixes compared to Firefox 35.0 released almost four years ago on January 13, 2015. https://www.mozilla.org/firefox/releases/

You do not have any real web browser options with the EOL Windows Vista as Chromium, Chrome and Opera dropped support of Vista (and WinXP) back in April 2016.

Thank you all for your help. I am sorry I took so long to respond; years ago I asked for help regarding something different and it went unanswered for some time, so I delayed looking back here. I have attempted to download the "52.9.0 esr" release, both the swedish release and the american release, several times, but the download keeps aborting. There is no issue downloading other releases.

If you can't get this page to work;

https://www.mozilla.org/en-US/firefox/52.9.0/releasenotes/

Then try a download from the Content Delivery Network, by default it should give you the US version;

https://download.mozilla.org/?product=firefox-52.9.0esr-SSL&os=win

Don't be alarmed, but that link will 'just download' the file rather than giving you a link to click on first.