One of the previously annoying limitations of Amazon S3 was that youcould not specify things like Content-Disposition on a per-request basis. If we use an MP3 as an example, if you uploaded it without a Content-Disposition header set, viewing it in a browser via the S3 URL would likely have your browser playing it rather than downloading. This behavior varies based on browser, but the big point is that it lead to inconsistency and confused some less technical users (“What do you mean I need to Right-Click then Save As?”).
Response Headers over GET to the Rescue!
This is recent, but breaking news. Googling around, it seems like this went largely unnoticed by many, so I’ll bring it up again here. You can now specify headers for GET requests for keys/objects as URL parameters. The response from S3 will have your provided headers instead of whatever was set at the time of upload (or not at all).