If you find jinitator not working on your windows machine, I recommend you to follow this link by RAYMOND REID to get this sorted.
Raymond recommends you to install the jiniator in windows compatibility mode as usual and then replace jvm.dll which reports error with an alternative jvm.dll in jinitiator directory (C:\Program Files (x86)\Oracle\JInitiator 220.127.116.11\bin\hotspot\).
Firefox 4.0 is still being built for a better performance and there is loads of improvements coming for users. If you wish to experience it right-away, you can download the nightly updates from nightly.mozilla.org or you can use the following ppa. sudo add-apt-repository ppa:ubuntu-mozilla-daily/ppa ; sudo apt-get update ; sudo apt-get install firefox-4.0 firefox-4.0-gnome-support