I'm using a plugin on my Mac called "Keyboard Maestro". How I use it: I have 2 Firefox windows open in one screen, side by side. I select an email address in window 1. I press the keyboard shortcut that activates keyboard Maestro. Maestro then copies the e-mail address, hits Command+` to switch to window 2 of Firefox. It then hits Command+T for a new tab, and types in a URL. Behind the URL it then hits Command+V to paste the e-mail address, and then hits enter. This allows me to select an e-mail address in window 1, do the keystroke, and immediately find this e-mail address on an admin page I use for work. (instead of copy, open website, paste, hit search). Now the bit where it's typing the address URL (needs to be a new tab) is lagging a lot since Firefox 4! In Firefox 3, the typing was blitzing fast. I tried the same keystroke in 2 windows of Safari: blitzing fast like Firefox 3. I then tried opening Firefox 4 again: slow again. I then experimented by typing really fast (just gibberish, but as fast as my fingers could move), and I noticed: Firefox4 address bar can not keep up with my typing speed. So there's the error. Typing the same speed in Safari and Firefox3? No problem, it keeps up. I have 2 add ons running, Xmarks 3.9.7 and Gmail Favicon Notifier 3.10.2 I don't think it's my Mac, as the typing speed does not lag in Safari or Firefox 3.