4.0.1 for windows in US English: http://releases.mozilla.org/pub/mozilla.org/firefox/releases/4.0.1/win32/en-US/

all others, can be found here: http://releases.mozilla.org/pub/mozilla.org/firefox/releases/

Firefox 4.0.1 is the latest version of Firefox 4 because it is no longer maintained.

Contact your fingerprint reader manufacturer.

If you do want to use it, install Firefox 3.6 that is still maintained.

Thanks for the help, guys.

How much of a risk am I taking if I just keep running 4.0.1?

THANKS so much for this answer! I must use LinkWad for work, and once I upgraded, I lost it, my boss has been furious at me all day. Hey Developers: When you sort out the bugs, I'll upgrade again, BUT I'll be sure to check the compatibility of my core programs first. THANKS again!

Wow, this is amazing. I have forced myself to wait on an upgrade to Firefox 4, because my fingerprint reader software was no longer supported. Works great with 3.6.??????. I finally get a solution from EgisTec, that has created an update to the HP SimplePass Fingerprint Software and it works semi-great with Firefox 4. And now Mozilla is trying to force-feed me Firefox 5 which is not compatible with the fingerprint reader software - AGAIN. When will you people learn? Maybe I should just go back to paper for all my account statements and devastate the rain forest.

If it's an extension, it probably still works just fine with Firefox 5.0. However, because of Firefox' poor compatibility design, until the editor releases a new version, you need to install Mozilla's Add-On Compatibility Reporter extension from https://addons.mozilla.org/en-US/firefox/addon/15003 and restart Firefox twice to check if it now works.

Each extension specifies the maximum compatible version, which is probably 4.0 in your case as Firefox did not give devs any time to verify and re-release their extensions for version 5.0.

The Add-On Compatibility Reporter extension basically tells Firefox to ignore the maximum compatible version so the extension can still work on version 5.0, just like it did on 4.0.

I think it is better for security reason to stick to Firefox 5.0 and try this workaround rather than downgrading to an earlier version. Tell us how it worked.

My fingerprint reader extension did not work with 5.0 even with the Add-On Compatibility Reporter. So, I tried 3.6.18, and it didn't work with that either! So, I'm back to 4.0.1.

What are my risks by staying with 4.0.1?

The risk of using a browser with security issues is to give to untrusted sites an access to some parts of your hard disk: http://www.mozilla.org/security/known-vulnerabilities/firefox.html#firefox5