From MozillaZine Knowledge Base
If you are trying to download or view a page from a site and instead it shows as gibberish/garbled text/garbage or includes HTML code, it's most likely the result of a misconfigured server sending the page with the wrong MIME type. For example, if an HTML page is sent with the MIME type "text/plain" instead of "text/html", the HTML code will be displayed as text. (You can find the MIME type of the page using "Tools -> Page Info" in Firefox or "View -> Page Info" in Mozilla Suite.)
- Contact the webmaster of the site and tell them about the issue. This is very important so that not only you can download/view the file properly, but others can too.
- Instead of clicking on the download/view link, right-click on it, pick "Save Link As", give it an appropriate name and extension, then open it locally.
- Alternately, open the gibberish file, then choose "File -> Save Page As", give it an appropriate name and extension, then open it locally.
Read Properly Configuring Server MIME Types
Related bug reports
- Bug 217905 — eagames.com - serving .shtml as text/plain
- Bug 261263 — validate charset (esp. UTF-8) of text/plain downloads (first N bytes) before accepting as text/plain