It may be you have a third party Firefox. OR this is a FAKE MESSAGE TO DOWNLOAD A VIRUS! Any time you want to check if a program is up to date;

1) Run the program and have it check for updates.
2) Go to the web site of the owner of the program and check
   there, or just download the current version listed.

That are scam messages and you shouldn't respond and click such an alert or you end up with malware.

Only download and install Firefox from the Mozilla servers.

How do I make sure its a Mozilla server?

I just got acquainted/infected with this one.  I almost fell for the request to update because it looked legitimate, but did not download it.  But I think I got it anyway. 

I run Malwarebytes Anti-malware Pro, AVG Pro, and ccCleaner.

And I don't think they are able to remove it... Even after just running them all, my computer has become slow booting up. Top and bottom blue border areas are wider than normal and do not look right.

Also, my Firefox says it is version 25.0.01 and is up to date. I have 64 bit Windows 7. Is there a version 26 ?

Firefox 26 is currently in beta and will be released next week.

• https://wiki.mozilla.org/Releases

rollie410, for starters as Firefox is not just for Windows but also Mac OSX and Linux, the Firefox updates are not ever done by way of a small .exe as this site claims.

The new versions is either done as a update in Firefox or by installing from www.mozilla.org