Native 64-bit builds of Firefox 4 Alpha for Windows are now appearing in the Firefox Nightly builds, and are expected to be released simultaneously when Firefox 4 ships.
Mac and Linux users have had 64-bit builds since early April, but there is still limited plug-in support, with most plug-ins falling back to 32-bit.
“This is still just a very very very early experimental build” noted Mozilla’s John O’Duinn. This means the browser may not behave as expected, and testers are advised to proceed with caution.
Eager testers can download 64-bit versions form the Firefox Nightly repository.