This site says you enter the following into the terminal and restart Safari:
defaults write com.apple.Safari DebugSnapshotsUpdatePolicy -int 2
Revert using:
defaults delete com.apple.Safari DebugSnapshotsUpdatePolicy
The site says it works with Safari 4. Let’s see if it works with Safari 5.
See also “Secrets” at BlackTree.
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via blog.vucica.net