Media File Viewer

Media File Viewer – See documents and media with the correct type

When you open files on large document sites, links often have wrong or generic types (like “application/octet-stream”). The browser then doesn’t know if something is a text file, image, or video, so it may download it, show a blank page, or fail to play it.

Media File Viewer fixes that. It detects the real file type by reading the file’s content (magic bytes), then lets you open or preview the file with the correct type so you can view or play it properly.

What it does

1. Detect the real file type
Click “Determine File Type of This Page” while you’re on a file or document page. The extension fetches the beginning of the file and checks its magic-byte signature (the same idea as the file command). It doesn’t rely only on the URL or the server’s Content-Type, so you get the actual format.

2. See what was detected
You get:
Detected MIME type (e.g. video/quicktime, audio/mp4)
How it was detected (e.g. “Magic bytes (Content-Type was generic)”)
HTTP status code and file size
So you know what the file is before opening it.

3. Open with the correct type
Use “Open in New Tab with Correct Type.” The extension rewrites the URL to use the correct file extension and opens it in a new tab. The server then typically serves it with the right MIME type, so the browser can display or play it instead of treating it as a generic download.

4. MOV handling
Many document sites host .mov (QuickTime) files. Browsers usually can’t play them directly in a tab. The extension:
Warns you when the detected type is QuickTime and explains that it can’t be shown in a normal tab.
Suggests using the Video Preview tool or opening in a new tab to download and play in another app.

5. Video preview
For video links, you can paste the URL into the “Video Preview” area and click “Load Video.” The extension fetches the file (using the page’s context so it works with the site’s access rules), then:
If the format is natively playable, it plays in the built-in player.
For MOV, it can convert the file in the browser (using FFmpeg.wasm) so you can preview it inside the extension without leaving the page.
That way you can quickly check video content without downloading or opening external apps.

Why install it
Accuracy – Type is determined from file content, not from misleading URLs or generic server headers.
Fewer failed opens – You see the real type first and open with the right extension, so the browser is more likely to display or play the file.
Transparency – You see MIME type, detection method, status code, and size before opening anything.
Video-friendly – file is detected and explained, and the Video Preview (with optional conversion) lets you watch videos in the extension.
Scoped and simple – It only runs on the two supported document sites, so there’s no broad access to the rest of your browsing.

If you often work with documents and media on justice.gov and run into wrong or generic file types, Media File Viewer is built to make viewing and playback reliable and predictable.

How to use
Go to a file or document URL on one of the supported sites.
Open the extension popup and click “Determine File Type of This Page.”
Check the detected MIME type and details.
Use “Open in New Tab with Correct Type” to open the file with the correct extension, or use Video Preview and paste the URL to load and (if needed) convert and play video in the popup.