2.53.4:
Made the Tabs bar a little higher in both the browser (Navigator) and the mail client (Messenger)
Removed the LEGACY warning link in the Add-ons manager when run stand-alone.
Improved the Lightning "Today Pane" button in Messengers statusbar.

2.53.5:
Changed the Lightning "Today Pane" button in Messengers statusbar.
Improved the "List all tabs" button in Navigators and Messengers tab bar.
Improved the scroll arrow buttons in Navigators tab bar.
Improved the Lightning tabs toolbar.

2.53.5.1:
Fixed themes for these pages:
about:performance
about:networking
about:debugging
about:profiles
about:support
about:memory
about:cache

2.53.6:
Updated Newsgroup subscription dialog