One obvious drawback of using this keyword is lack of flexibility. You need to modify the source code to use it and modify again to get rid of it.
A problem has come up when you need to debug a code that contains
debugger keywords and you can't remove it. And this is where Firebug can become handy tool again.
See all Firebug tips
Let's image following script:
If onClick method is executed Firebug shows following bubble that offers disabling.
The 'Do not display...' check-box has been introduced in Firebug 1.7a10.
If you pressed the Disable button, a disabled breakpoint has been created on the same line. A breakpoint has higher priority over
debugger keyword and since it's disabled it also effectively disables the keyword.