You can use CSS to accomplish this in most browsers: http://jsfiddle.net/fQthQ/
* {
-ms-user-select: none; /* IE 10+ */
-moz-user-select: -moz-none;
-khtml-user-select: none;
-webkit-user-select: none;
user-select: none;
}
.selectable {
-ms-user-select: auto;
-moz-user-select: auto;
-khtml-user-select: auto;
-webkit-user-select: auto;
user-select: auto;
}
Opera does not currently support this feature.
See the MDN page for more info: https://developer.mozilla.org/en-US/docs/CSS/user-select