I’ve been experiencing some slowness of late working with WordPress (specifically the admin dashboard) on Firefox 3.5. Opera and Safari seemed to be just fine, but it has been taking a really long time lately to do things like bring up the “Edit Page” admin page.
It finally got annoying enough that I had to get it fixed. Google is your friend, of course, and a quick search led me to this forum post on wordpress.com. It pointed me towards Firefox extensions being the problem. I only run two FF extensions namely: the Web Developer add-on and the great Firebug. I disabled them both and low and behold, the slowness with the WP admin pages was gone. Unfortunately, I consider neither of those plugins dispensable, so had to re-enable both of them. Just to determine which one was causing the slowness, I enabled them one at a time, but the slowness didn’t come back. I’ve got both my plugins back in place and the slowness issues have gone away. Go figure.