From the first and second post of redarnet, it appears that 'Safari' can be launched (opened, run) and used to surf the internet. However, it intermittently may crash.
The downloading of files, including '.mp3', is strictly a 'Safari' function; and, are not related to 'QuickTime' in any way. The playing of some website based files - '.mp3', '.mov', '.wav', etc. are dependent on 'QuickTime'.
Inside the '/Library/Internet Plug-Ins/' folder there should be a 'QuickTime Plugin.plugin' (version 6.x) file (due to the back-installation of 'Quicktime 6.5.2').
If a 'QuickTime Plugin.webplugin' (version 7.x) also exists - move it to your 'Desktop', and reboot (restart) your Mac. Try 'Safari', doing what you normally do. Any more crashes? If not - trash the 'Desktop' based 'QuickTime Plugin.webplugin' file.
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