I was having some problems with ff (hanging and greying out on page load/refresh, downloads stuck at 0% until I killed and restarted ff, etc.), so I just reinstalled it and, with just abp plus utilities (dev builds) freshly installed I got this on filter prefs dialog, when switching focus to easylist (but not on abp warning removal list):
A script on this page may be busy, or it may have stopped responding. You can stop the script now, open the script in the debugger, or let the script continue.
This dialog only shows since I reinstalled, but problem was there before.
I'm using nightly x64/win7.