Firefox Beta and Developer Edition
Release Notes

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

Windows 7+ users on 64-bit OS can select 32-bit or 64-bit versions in the stub installer

Updated the design of site permission requests to make them harder to miss and easier to understand

Windows XP and Vista are no longer supported. XP and Vista users running Firefox 52 will continue to receive security updates on Firefox ESR 52.

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

The last few characters of shortened tab titles fade out instead of being replaced by ellipses to keep more of the title visible

New visual design for audio and video controls

Ended Firefox Linux support for processors older than Pentium 4 and AMD Opteron

Media playback on new tabs is blocked until the tab is visible

Changes for web developers

Support for WebM video with alpha, which allows playing videos with transparent backgrounds