You should contact Norton support about their false positive detections or stop using Norton. This is beyond Firefox browser issue and is a Norton issue.

The message is because your Firefox is routing a request for that file through Norton Safe Web.

Now the question is why Firefox is requesting a file from that site. Usually it would be a request in one of the pages that is currently open in a tab. Can you recall what page you opened before this started? Do you have any tabs open that you don't need any more and so you can close them?

You didn't share your browser data, but another possible culprit would be an extension. You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• 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.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Then cast a critical eye over the list below that heading. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

Any improvement?