Mozilla has published Firefox 23, you can download it over here or wait for the automatic update if you already have Firefox.
Other notable changes include a new network monitor feature for developers, as well as the removal of the blink HTML tag. This HTML tag was a non-standard element that was quite popular in the early days of the web but it's been dead for a long time. Internet Explorer never supported it and support for the blink tag was already removed from WebKit (Chrome/Safari).
Here's the full overview of what's new:
NEW - Mixed content blocking enabled to protects users from man-in-the-middle attacks and eavesdroppers on HTTPS pages (learn more)
NEW - Options panel created for Web Developer Toolbox
CHANGED - Updated Firefox Logo
CHANGED - Improved about:memory's functional UI
CHANGED - Simplified interface for notifications of plugin installation
CHANGED - Enabled DXVA2 on Windows Vista+ to accelerate H.264 video decoding
CHANGED - Users can now switch to a new search provider across the entire browser
CHANGED - CSP policies using the standard syntax and semantics will now be enforced