Firefox has the annoying habit of popping up an error message after 5 seconds (10 seconds for Firefox 2.x) when running Javascript code. This causes lots of irritation because a) some script genuinely need more than the default time, b) the error message pops up repeatedly after every 5-10 seconds thereby severely ruining your browsing experience and c) the strangely worded warning where Cancel is what allows you to continue responds very sluggishly and looks like hanging even on my Core 2 Duo machine. Fortunately there is a simple fix. With the current plethora of Web 2.0 applications I am sure you will need this sooner or later.