Stop Scrollbars from Disappearing

In OS X Mountain Lion the scrollbars are invisible unless you scroll the document or simply place two fingers on the trackpad. This leaves those who like to click and grab the scroller in the lurch, because if you move the mouse cursor to where the scrollbar usually is, there’s nothing there—both the ver- tical and horizontal scrollbars (if the window has one) remain invisible! 

Within System Preferences (Apple menu→System Preferences), you can opt to always have the scrollbar always visible—click the General icon, and select Show Scroll Bars. This is certainly a solution but not an elegant one.

Viewing Scrollbars When the Cursor Hovers Over Them

Luckily there’s a secret setting that allows the best of both worlds—it will cause the scrollbars to appear when your mouse cursor hovers over the edge of the window (or bottom, if the document you’re viewing scrolls horizontally). Otherwise, the scrollbars be invisible unless you’re scrolling through the document, as mentioned earlier.

To activate the secret setting, open Terminal, and type the following:

defaults write -g NSOverlayScrollerShowOnMouseOver -bool TRUE

Then log out and back in again for the changes to take effect. 

Note that if this doesn’t seem to work and you’re using a standard PC mouse, you might also have to switch the Show Scroll Bars setting in System Preferences, as mentioned earlier, to When Scrolling.

Deactivating Scrollbars-on-Hover

To deactivate the new feature, again open a Terminal window, and type the following:

defaults delete -g NSOverlayScrollerShowOnMouseOver

Then log out and back in again for the changes to take effect.