Sorry, no, that is malware. New sites have been popping up every day for a month pushing that fake patch. They all use "phishing" techniques to try to convince users that it's a Mozilla page, but the addresses give away the deception. (As you probably know, Firefox never advertises updates in a tab that way.)

Hopefully you did not download it or run it.

If you downloaded it (but didn't run it), please delete the download very carefully as follows:

When you are using the downloads panel (the one attached to the toolbar button), be careful not to click anything as that may run it. Instead, right-click it and choose Open Containing Folder. That will launch a file window with the unwanted download highlighted, and then you can press the Delete key to send it to the Windows Recycle Bin.

If the download has already disappeared from the panel, the same mouse action works in the full download list (Ctrl+j or "Show All Downloads").

If you already ran it, please delete the download and also use the free cleaning tools in our support article: Troubleshoot Firefox issues caused by malware.

Over the next few days, many users will get a prompt about Firefox 48.0 being available. The notification should look completely different from the fake patch page.

To update safely, when you're ready, see this article: Update Firefox to the latest release.