Firefox desktop · Research guidance. Instructions are based on publisher guidance; a UK IPTV account was not tested on this platform.
Identify the download entry
Use Firefox’s Downloads button to inspect the intended item rather than repeatedly clicking the original website link. Check the filename and current status. Multiple attempts can produce several similarly named files, making it difficult to know which one an application tried to open. Keep the observation tied to one entry.
Separate a warning from a completion
Mozilla documents download protection for malicious, unwanted and uncommon software, along with blocking insecure downloads. A warning deserves its own review; it is not simply a missing default application. Read the explanation associated with that entry and verify the publisher’s distribution route before deciding what to do next.
Review the configured action
Firefox’s Settings include a Files and applications area in the General downloads settings where supported file types can have an opening action or an ask-each-time choice. Use the actual file type shown there. An application selected for one type does not establish that every file with a similar name is the same format.
Use a harmless comparison
For a file you own and trust, check whether the completed file can be located and opened by the intended application. This isolates a browser handling question from an account or streaming question. Do not use a private playlist as a public test attachment, and do not rename a suspicious executable to resemble a media file in an attempt to bypass its warning.
Questions, answered
Does a completed download necessarily have a suitable app?
No. Saving the file and handling its format are separate steps.
Is a warning just a default-app error?
No. Read the actual download-protection explanation.