How can I guaranteed, 100% ,absolutely etc. focus URL in Firefox browser?
If there is Flash on page that focus is on it and CTR-L doesn't focus URL.
Sorry, the Flash portion is another application which handles all of your hot-keys (even tab switching).
To guarantee you need to use your mouse to click outside the flash element. The only reasonable surround I can see is to use AutoHotkey to emulate a mouse click so it can be done by keyboard...