Maybe you created your own custom button from divs, or you just want to disable the ability to select text on an element (Usually is used for elements that act like buttons).

-webkit-user-select: none;
-khtml-user-select: none;
-moz-user-select: none;
-o-user-select: none;
user-select: none;

Use all these selectors on the element. This should work on all browsers.