You may have found that since upgrading to OS X Lion, your browsing experience with Safari has changed slightly. Your web page could be jumping out at you for no obvious reason. You might just be unknowingly double-tapping your mouse, causing the page to zoom. Touch sensitivity in Lion is greater than it was in Snow Leopard by default. By double-tapping a second time, you should be able to put things right again, but here are a few tips for correcting this behavior:
1. Disable zooming in mouse preferences
If this is really annoying you, simply disable this feature entirely. You can do this by unchecking the Smart Zoom feature on the Point & Click settings in the Mouse section of System Preferences.
2. Install a better preference configuration tool
On the other hand, if you do want to use your touch sensitive mouse to its fullest potential, consider installing either MagicPrefs or BetterTouchTool. Even if you’re not having problems, you may find either of these two tools very handy. Both tools are free and have recently been updated to allow the user to take much more fine-grained control over their touch experience on OS X Lion. For example, with BetterTouchTool, you can control the sensitivity of the Magic Mouse, and how it registers touch events.
3. Replace your mouse with a Magic Trackpad
Finally, it may be time to just get rid of that antiquated input device called a “mouse” and get a Magic Trackpad. Even if you have a MacBook, you may find the location of the Magic Touchpad to either side of the keyboard more ergonomically comfortable than to have it sandwiched in the middle front of the keyboard. Personally, I’ve found that I use my Magic Trackpad far more often in OS X Lion than I use my Magic Mouse, even though the situation was reversed when I was using Snow Leopard.