I'm using Firefox for web development, and set breakpoints with the `debugger` keyword, or the breakpoint UI in the "Debugger" section of the "Web Developer" tools. I remember that used to work on older versions, but recently it started failing. Now, when I enter debugging mode (i.e. hit a breakpoint), the debugger UI shows, but it is completely unresponsive: the mouse cursor doesn't change when I hover over any widget, and clicking does nothing. The only way to get any response is CTRL-r refresh which *sometimes* works, as well as closing the entire Firefox window. Of course, that means I can't actually use it to debug. I'm on Xubuntu 13.10, running latest stable 64bit Firefox (3.1.1). I also verified the exact same bug on the nightly binary release (firefox-36.0a1.en-US.linux-x86_64.tar.bz2) as well as the recently released Developer Edition (firefox-35.0a2.en-US.linux-x86_64.tar.bz2).