I assume this problem is in Firefox on Windows 10, even though your question is posted under Firefox Focus, which is a mobile app.

You are right to be cautious about any popup suggestions to install any kind of software.

You can check whether your McAfee software included an automatically installed Firefox add-on - open the Add-ons page using either:

• click the Extensions button (puzzle piece) on the toolbar > Manage Extensions
• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading.

Can you see a McAfee extension either in the Enabled or in the Disabled section?

If it's not there, please check with McAfee directly using a trusted address like

https://www.mcafee.com/support/s/global-search/firefox%20extension?language=en_US

If you do not use and do not want to use McAfee software, please ignore the ads. If you are getting notifications from websites advertising this software, you can remove notification permission using the Settings page. See:

Web Push notifications in Firefox - See "How do I revoke Web Push permissions for a specific site?"