On spam susceptibility and browser updating
You can always manually check for Firefox updates - to learn how, see Update Firefox to the latest release.
If you start Firefox and see a notification bar with a Heartbeat icon, the message button, this is a legitimate Firefox update notice and you should update Firefox.
Some people have also reported seeing ads prompting them to download a Firefox update or occurrences of fake 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.
You can upgrade to a newer version of Internet Explorer. You could get a virus by just viewing a malicious website.
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.
This is an example of what a fake Firefox update notice might look like.
These are hosted on randomly generated and quickly changing domains: 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 (see below).
This is just one example in a constant stream of very similar Pay Pal phishing messages.
To learn more about the "Heartbeat" feature, see the article Rate your Firefox experience, surveys and out of date messages (Heartbeat) and this Mozilla Wiki page.