For some reason, you are getting directed to the Mac update.

• Changes between 5.0 and 5.0.1 (click "What's New in Firefox"): https://www.mozilla.com/en-US/firefox/5.0.1/releasenotes/

NOTE: There is no difference in Firefox 5.0 and 5.0.1 for Windows or any OS other than OSX. The version number had to be changed for all OSes because the update server is unable to handle multiple current release numbers based on the OS. For all OSes the current release number must be the same.

You might as well wait until tomorrow, 2011-08-16, when Firefox 6 is due to be released. Most changes in Firefox 6 are "under the hood", not in the interface.

• Preliminary information about Firefox 6 (click "What's New in Firefox"): https://www.mozilla.com/en-US/firefox/6.0/releasenotes/
• NOTE: DO NOT DOWNLOAD THE BETA. You will be switched to the beta channel if you do and you will be updated to new beta versions only if you do so.
• WAIT UNTIL you receive the update notification; or beginning late tomorrow or Wednesday you can begin checking in your Firefox 5 with Help > About Firefox > Check for Updates to get the RELEASE version of Firefox 6, not the beta.

If this reply solves your problem, please click "Solved It" next to this reply when signed-in to the forum.

Not related to your question, but...

You need to update some plug-ins:

• Plug-in check: https://www-trunk.stage.mozilla.com/en-US/plugincheck/
• Adobe PDF Plug-In For Firefox and Netscape: Installing/Updating Adobe Reader in Firefox
• Shockwave Flash (Adobe Flash or Flash): Updating Flash in Firefox

Thank you, SafeBrowser. My problem is solved, as long as I have FFox 5.0 (win32). No need for me to have ver.5.0.1 .

   But I think, users with version 4.xx also will get messages "You have most recent Firefox". Because of browser looks for update into national subfolders of:

http://releases.mozilla.org/pub/mozilla.org/firefox/releases/latest/update/win32

  and will not be updated.
      Time is cure! Tomorrow (August 16) they also will be happy, when version 6 will create this new folder "... latest/update/win32" (near mac-folder).
      Thank you for excellent reply, SafeBrowser.
SOLVED

Correct link is http://releases.mozilla.org/pub/mozilla.org/firefox/releases/latest/win32/