After upgrading to Firefox 3.5, I noticed that I started getting this warning with some sites after a long delay:
A script on this page may be busy, or It may have stopped responding. You can stop the script now, or you can continue to see if the script will complete. It only happened with some sites, like Google Maps, Twitter and Meetup.com, but it was really annoying. Also I noticed that sites which made use of Google Analytics often paused when contacting an Analytics server. Because I do a lot of web development, I have a lot of add-ons installed in Firefox. Disabling all add-ons got rid of the problem, so I knew that one of them was to blame.
I went a’Googling and found a page dedicated to the error on the MozillaZine site. That page lists a number of Firefox add-ons that are known to cause this error. Imagine my surprise to see Extended Cookie Manager on the list. I’ve been using that add-on for years, since version 1.x, to allow me more finely grained control over the cookies that sites set. It didn’t cause this problem in the past, so I wasn’t sure that it was responsible now.
I disabled Extended Cookie Manager and tried Google Maps and Meetup.com. Both appeared quickly, with no delays when navigating around the site. I had been forced to use other browsers for months to avoid such problems, and now they were back to normal. I had my culprit.
A quick visit to the Add-ons directory yielded Cookie Monster by Tony Schilling. It does everything that Extended Cookie Manager did and more, without slowing down Firefox.
It’s too bad that I had to switch, but Extended Cookie Manager hadn’t been updated in over two years, so its future looks dim. Check out Cookie Monster and enjoy surfing without errors.