使用content-disposition提供的文件：内联有时会提示下载

My subject line says most of what I'm asking. I've got a web site that outputs reports in various formats (HTML, CSV, TSV, Excel, etc). Whenever possible, I'd like these files to be shown in the browser. To that end, I've set up my headers so that "Content-Disposition" is "inline". This works very inconsistently with different file types. It seems that in both FF3 and IE7, HTML will always open inline automatically. That makes sense. If I use TSV, both browsers will prompt for download, since it's an unknown file type on my system. That also makes sense and is exactly what I want. Excel and CSV, however, offer different behaviors. In FF, both always prompt for download or opening. If I choose "open", it opens in a new window. In IE, both My subject line says most of what I'm asking. I