Firefox 23 also comes with a new logo, see below for Firefox's logo evolution:

Firefox 23 has been officially released on Firefox.com and all existing users should be able to upgrade to it automatically. The Android version is available on Google Play.
The biggest addition to Firefox 23 is the share button and the browser's Social API. Developers can let users share content with friends with only one click.
Here is the social button in action:

Also included is the mixed content blocker, which prevents nonsecure (HTTP) content on a website being read or modified by attackers by blocking the nonsecure content from being compromised. In case you’re wondering, mixed content occurs when a webpage containing a combination of both secure (HTTPS) and nonsecure (HTTP) content is delivered over a secure data channel to the browser. Here’s how it looks in action (more details are available here):
Firefox for Android also includes the new logo, but it has a slew of its new features specific to Google’s mobile platform as well.
The full Android changelog isn't available yet.
Firefox 24 is expected to come out in September.
Firefox Changelog:
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: “Enable JavaScript” preference checkbox has been removed and user-set values will be reset to the default.
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.
CHANGED: rendering improvements (see bug 838675).
CHANGED: Replace fixed-ratio audio resampler in webrtc.org capture code with Speex resampler and eliminate pseudo-44000Hz rate.
CHANGED: “Load images automatically” and Always show the tab bar” checkboxes removed from preferences and reset to defaults.
DEVELOPER: HTML5 form control implemented.
DEVELOPER: Write more accessible pages on touch interfaces with new ARIA role for key buttons.
DEVELOPER: Social share functionality.
DEVELOPER: Added unprefixed requestAnimationFrame.
DEVELOPER: Implemented a global browser console.
DEVELOPER: Dropped blink effect from text-decoration: blink; and completely removed element
DEVELOPER: New feature in toolbox: Network Monitor.
FIXED: Various security fixes.