As a last resort to crashing and performance issues with Safari 5.0, you can downgrade to Safari 4.0.5. Unfortunately, although Apple maintains a Safari 4.0.5 download page, the Safari 4.0.5 installer installer will not run once Safari 5.0 is installed, stating that an older version of Safari cannot be installed over a new one.
To get around this problem, you’ll need to use one of the following options:
Archive and Install Mac OS X Use your Mac OS X installation disc to perform an archive and install process as described here. Install all available updates except for Safari 5.0. Instead, download Safari 4.0.5 from this page if that version is not installed by your Mac OS X disc.
Force install Download Pacifist and the Safari 4.0.5 installer. Drag the Safari 4.0.5 installer package onto the Pacifist application icon to open it.
Once the Safari 4.0.5 package is open in Pacifist, select it from the list, then click “Install” in the upper left corner of the Pacifist window. Leave the “use administrator privileges” box checked.
You’ll be presented with a dialog box that states “Application already exists.” Check “Don’t ask again for this installation” then click “Replace.”
After performing this process, restart your Mac. You’ll be left with an earlier version of Safari.