i mean, how to turn it on, as the elements should be selected with mouse click, like in OPERA. (i know, there is such option to "select with mouse click" in FF and Chrome, but they are turned on only for first-click, and the second mouse click wont selects an element). how to turn it on permanently?
With FireBug I have found Ctrl + Shift + C will enable inspect mode on the fly if you are good with keyboard shortcuts.
If you use FireFox's Developer Console Ctrl + Shift + K then after clicking on an element there is a box leftover with an Inspect icon