We have received reports from many users who were interrupted in their browsing experience and who got redirected to a fake page pretending to provide an "important", "urgent" or "critical" update. Some people have also reported seeing ads prompting them to download a Firefox update or occurrences of fake Firefox requires a manual update pages that try to trick them into installing a malicious extension.These are scam tactics to trick you into installing malware!

Note: If you start Firefox and see a notification bar with a Heartbeat icon, the message Your Firefox is critically out of date. An update is required to stay secure and an Update Now button (as shown below), this is a legitimate Firefox update prompt. Please follow the download to update Firefox.

For more information about the "Heartbeat" feature, see the article Rate your Firefox experience, surveys and out of date messages (Heartbeat) and this Mozilla Wiki page.

Firefox has an automated background update mechanism which will never prompt you to manually download and execute a file, except in the case of a Heartbeat notification (as shown above). You can always check for updates within Firefox yourself - to learn how, see Update Firefox to the latest release.

To our knowledge, fake update notices are a form of "malvertising". Those fake notices get triggered by code contained in ads that are displayed on otherwise legitimate websites you are visiting and get spread through advertisement networks.

This is an example of what a fake Firefox update notice might look like. These are hosted on randomly generated and quickly changing domains:

What you can do if you spot a fake update notice?

1. Never click on these fake update notices.
2. Never save or open/run unsolicited files!
3. Install an ad-blocking add-on from addons.mozilla.org to avoid such kind of malvertising in the future.
4. Report web forgeries to the Google Web Forgery site.

What you can do to prevent malware on your computer

1. Run a malware scan on your computer to make sure your computer was not infected. (See Troubleshoot Firefox issues caused by malware.)
2. Avoid downloads from unreliable sources in the future.
3. Use What happened to Tracking Protection? (also available in Private Browsing).

To learn more about malware

• Kaspersky Internet Safety
• AVG "Is it Malware?"
• Apple Forums advice on if you have malware

Fake updates have been spotted for other popular browsers. Although we cannot root out every bad actor on the web, we are continuing to improve Firefox's defenses against malware. Knowing how to recognize and report such frauds helps us keep the Internet open and safer.