The newest Firefox is version 40, and as usual there was no proper announcement. There’s a post on the Mozilla blog that gets into the details of version 40’s security improvements, but it never mentions the version. The release notes provide additional details. Here are some of the more notable changes:

• Improvements to Windows 10 support, including workarounds for the way Microsoft messes up default browser settings
• Add-on certification: non-certified add-ons will be disabled by default
• Improvements to visual style: for example, the ‘close’ button on tabs is now larger
• Expanded malware protection, which warns users about to visit sites that are flagged by Google’s Safe Browsing Service
• Smoother animation and scrolling for Windows
• Improvements to JPEG image handling
• At least fourteen security fixes