Mozilla’s developers still haven’t succeeded to create a stable 64-bit version of the Firefox browser. Also version 41 of Firefox will be a 32-bit Windows application. The culprit is the Windows NPAPI process sandbox which should make sure that plugins run better and more stable. Mozilla introduced the sandbox in January this year but continues to find issues with the implementation.
The developers considers the Adobe Flash plugin, which runs in the sandbox, not stable enough. Therefore the 64-bit version of Firefox 41 will only be released in the beta channel.
Mozilla offers a 64-bit version of Firefox for Windows since 2010 already, but only in early and unsupported Nightly releases. In 2014 the first stable release should have been become reality but it was withdraw before the release. This happened several times afterwards as well which is why some consider the 64-bit Firefox version as ‘Vaporware’.
The Firefox developers now aim to fix the NPAPI process sandbox issues in version 43 which is planned for the beginning of December this year.
Despite the fact that Firefox has not released a stable 64-bit version of the browser, there is a 64-bit Firefox fork that is considered stable called Waterfox.