This might be browser specific and therefore not work with older browsers

A simple change of the textbox type (text -> search) offers a nice little extra feature of clearing the textbox content with a single click.
The textbox doesn't even have to have the focus.

Alternative is to triple click the text and that sometimes doesn't work well.

It does not currently work for textboxes genereated after the page load (e.g. Quick Action Popups).