Comment 2 for bug 520049

I can confirm that I've just had this happen with Firefox 3.6.3. The user agent has been changed to "QuickTime/7.6.4".

This is running 10.04 with firefox 3.6.3+nobinonly-0ubuntu4 installed.

I noticed this problem after an unexpected exit of Firefox (i.e a crash) on a media-heavy site (http://wellthatsadorable.com/). I suspect that gecko-mediaplayer sets this value in order to convince a QuickTime streaming server that it can handle the media, then resets the value after the media is loaded. In the case of a crash the override value is left in place.

The reason for suspecting gecko-mediaplayer is that about:plugins shows:

QuickTime Plug-in 7.6.4
    File: gecko-mediaplayer-qt.so
    Version:
    Gecko Media Player 0.9.9.2

QuickTime Plug-in 7.6.6
    File: libtotem-narrowspace-plugin.so
    Version:
    The Totem 2.30.2 plugin handles video and audio streams.

The 7.6.4 version in the useragent string matches that reported by the gecko-mediaplayer plugin.