Firefox 53.0

What's new in this version:

New:
- Improved graphics stability for Windows users with the addition of compositor process separation (Quantum Compositor)
- Two new 'compact' themes available in Firefox, dark and light, based on the Firefox Developer Edition theme
- Lightweight themes are now applied in private browsing windows
- Reader Mode now displays estimated reading time for the page

Changed:
- Updated the design of site permission requests to make them harder to miss and easier to understand
- 32-bit Mac OS X is no longer supported. 32-bit Mac OS X users can switch to Firefox ESR 52 to continue receiving security updates.
- Updates for Mac OS X are smaller in size compared to updates for Firefox 52
- Media playback on new tabs is blocked until the tab is visible
- New visual design for audio and video controls
- The last few characters of shortened tab titles fade out instead of being replaced by ellipses to keep more of the title visible
- Media playback on new tabs is blocked until the tab is visible

Developer:
- Support for WebM video with alpha, which allows playing videos with transparent backgrounds
- More details on changes for web developers at https://developer.mozilla.org/en-US/Firefox/Releases/53#Changes_for_Web_developers