I have installed Firefox 4 in my Debian Testing installation from Launchpad PPA. It is quite stable and I have decided to use it instead of Firefox 3. Most of the addons I used is compatible with Firefox 4 by now. However, the version of Greasemonkey available in Mozilla Firefox Addons Site is not compatible with Mozilla Firefox v4 latest build. To install the latest nightly build of Greasemonkey, I went to Greasemonkey Nightly Download and installed it. However Greasefire is not available, we can install userscripts directly from Userscripts website for now.