What should I check before opening a file I downloaded from a website?

Start by checking whether the download matches an action you deliberately took. Did you choose this file from a page you meant to visit, or did it appear after an unexpected pop-up, redirect, or button click? If you cannot tell where it came from, do not open it just to find out.

Next, compare the file with what the page said you would receive. Check its displayed name and type, and whether those fit the purpose—for example, a document you expected rather than an unrelated-looking file. These checks can reveal a mismatch, but they do not prove that a file is safe.

Use your browser’s downloads list or panel to find the item and review what it shows about the download. In Firefox, the Downloads panel is where downloads can be viewed and warnings may appear. Mozilla says it can warn about suspected malicious or potentially unsafe downloads, including uncommon files. A warning is not proof that a file is safe. [S1]

If you do not recognize the page or the download was not something you intended, stop there. Don’t open the file to investigate it. If you need the file, go back to the site by using a route you already trust and check whether it offers the item you meant to get.

If the browser warns you, treat that as a reason to pause, not a prompt to bypass the warning. Mozilla describes warnings for downloads it suspects may be malicious or potentially unsafe. Its guidance says to stop rather than override the warning when the file was unexpected, its source or type does not match what you intended, or the browser warns about it. [S1]

A plausible name does not settle the question. Leave the download unopened if you are unsure, and ask someone you trust or the organization responsible for the website to help verify whether the file is expected. Don’t rely on the absence of a warning as a guarantee; the cited guidance does not establish that an unwarned file is safe.

Suppose you intended to download a form from a service you use. The page instead opens an unexpected download, and the browser flags it. That combination is enough to stop: don’t open it or override the warning. You could note the page you were using, the file’s displayed name, and the warning, then contact the service through a route you already trust and ask whether the file is expected.

That example is a cautious way to organize the decision, not a test that can certify a download. If the file’s source or type does not match what you expected, or the browser warns about it, stop and seek trusted support rather than trying to inspect or bypass it.

Before opening it, ask: Did I deliberately request this file, and does its source and displayed type match what I expected? Then check whether the browser has warned you. If anything is unexpected, mismatched, or flagged, leave the file unopened and ask a trusted person or the responsible organization for help.

These checks help you decide when to stop; they cannot establish that a file is harmless. If you are uncertain, not opening it is the cautious choice.