New laptop set up

The "alert messages" you are seeing in Firefox on your old Mac are almost certainly browser-based scams(tech support scams, adware extensions, or malicious notifications) rather than a deep, system-level virus. Because these usually live inside your browser profile, using Apple's built-in Migration Assistant or copying your entire user folder could transfer the bad files over.

Here is exactly how to safely set up your new Mac without bringing the problem along:

1. Do Not Transfer Firefox Data via Migration Assistant

When you turn on your new Mac, Apple's Migration Assistant will ask if you want to transfer data from your old Mac.

• Safe to transfer: Applications, Documents, Photos, and Downloads.
• Avoid transferring: Leave "Computer & Network Settings" or any custom system settings unchecked if given the option, as browser data resides inside your user library settings.
• The safest option: For complete peace of mind, choose not to use Migration Assistant at all for your user profile settings. Instead, manually transfer only your raw data files (like PDFs, Word docs, photos) using an external hard drive, USB flash drive, or cloud storage (like iCloud, Google Drive, or OneDrive). Raw files like photos and documents cannot carry these Firefox browser scams.

<< I keep getting alert messages when using Firefox. >>

Before you get too excited about this being "recently infected somehow", please use the old Mac and post a screenshot of one of these messages.

This is likely not an infection at all, just unwanted notifications.

You may be able to 'snuff them out' in fairly straightforward way before you start to transfer anything to the new Mac.

melanocarpa wrote:

My 10+ year old Mac laptop was recently infected somehow when using Firefox browser. I am ready to set up a new mac laptop that will arrive this week. I keep getting alert messages when using Firefox. Is there something I should do to avoid transferring that problem to the new computer when I transfer the data?

Set up your Mac to be secure

https://support.apple.com/guide/mac-help/set-up-your-mac-to-be-secure-flvlt003/macc

In general—

Protect your Mac from malware - Apple Support

Protect your Mac from malware - Apple Support

Recognize and avoid phishing messages, phony support calls

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

This User Tip article describes how to deal with unwanted notifications, if that turns out to be the issue.

It is a little complicated, but NOT DIFFICULT.

Stop unwanted Notifications - Apple Community

I already deleted Firefox fearing the worst. Now I cannot download it - trying to get the ESR version but it won't download. So I cannot post the messages. However, I think you are correct about notifications. I am using the safari browser for now and plan to download Firefox when I get my new mac laptop later this week. Thanks

Great advice. Thanks.