Mozilla has released the next version of Firefox, with Firefox 40 on August 11, 2015. There are several new features, fixes and changes with this release. See the Release Notes for full details. Users can get the updated version by going to the Help Menu within Firefox and selecting About Firefox, then follow the prompts. Users can also manually download the latest version of Firefox via the getfirefox.com site.
The next planned release is Firefox 41 on September 22nd. This release may include the 64-Bit version of Firefox for Windows.