I put your code into a simple test case, which I attached to this post. Using Firefox 31.0 + Firebug 2.0.3 on Win8.1.
The lines are correctly marked as executable, I can set a breakpoint at the line containing
if (x == 1) { and it also gets it when I reload the page.
I assume you have a syntax error within your script. When there is a syntax error within a script, you may not be able to set a breakpoint in it. So please check whether there are any JavaScript errors shown within the
Console panel (ensure you have the option
Show JavaScript Errors checked).
If you can exclude syntax errors as the cause, please
provide a complete test case and describe the steps to reproduce the problem.
Sebastian