The basic problem is that ABC files are sent by servers as several different MIME types. With servers that send text/plain, there is no problem getting the file treated as text, but you can't get the file recognized as music. The correct MIME type for .abc files is text/vnd.abc, and some servers are set up to send this type, but then most browsers refuse to deal with it at all until you explain what to do with it.
Some web servers send .abc files as some type other than text/plain or text/vnd.abc, often such things as application/octet or application/binary or audio/x-abc. For such cases, you'll have to experiment a bit. Or try to contact the webmaster and get the problem fixed.
The best-quality printed music is with PS (PostScript) or PDF (Portable Data Format), both proprietary data formats owned by Adobe. Unix systems usually come with software for these; for other systems you might want to get the latest versions of the free reader software:
Here's a table of summaries of what we've learned about particular OS/browser combinations:
|Macintosh||Internet Explorer 4.5|
|Windows 95/98||Internet Explorer|
|Description:||ABC music notation|
|Application:||xterm -e $EDITOR %s|
Scroll down the left-hand side of the "Preferences" window until you see an icon called "Helpers" and select it.
At the bottom right of the "Helpers" window, click the "Create Helper..." button.
In the top field, where it says: "Open files with the following MIME type:" enter: text/vnd.abc
In the next field, where it says: "Or the following suffixes" enter: abc
Next, where it says: "With the application program" click the "Select" button and navigate your way to BarFly or any other abc interpreter.
The check box at the bottom is optional. Click OK twice to close the "Helpers" set-up window and the "Preferences" window, and you're all done.
(Thanks to David Barnert for documenting this.)