Screenshots are anonymised. Thanks to Social Fixer for some of the anonymous names.

Summarised changelog (see git for full changelog):

2017-03-25: Style reactions and group polls. Fix mentions colours.
2017-03-24: Ensure the white border around message bubbles is gone when installed as a userscript.
2017-03-23: Remove the new white border around message bubbles. Fix the photo forward button.
2017-01-05: Fix the image info dialog text, thanks J3n50m4t.
2016-12-31: Fix group calling and the game picker.
2016-12-06: Quick fixes for game-related things. Fix the new sticker button icon and other subtle fixes.
2016-06-06: Fix new emoji selection. Fix the borders around profile photos in group chat icons.
2016-05-26: Fix search in conversation bar.
2016-05-23: Fix code bubbles.
2016-04-15: Update for Messenger Platform messages.
2016-03-15.2: Support chat colours, thanks macfeaster!
2016-03-15: Fix for when the style is installed as user JS. Style the clear search and message request icons to be actually visible.
2016-02-26: Fix the info panel headings and mute notifications checkbox label (again).
2016-02-20: Fix keyboard selection in search. Minor updates.
2016-02-07: Update for emoji-only messages.
2016-01-28: Fix the input bar (thanks again Facebook).
2016-01-26: Style the other login page. Misc updates (thanks Facebook...) and minor tweaks.
2015-12-10: Minor fixes.
2015-11-25: Fix the message requests notification. Style the call page.
2015-11-19: Fix the active people list. Minor tweaks and cleanups.
2015-11-05: Style part of the login page. Fix audio messages. Tweak chat sidebar colours. Tweak menu hover colour to be the same hue as other things. Style the media (GIFs) source app info.
2015-10-19: Slight tweaks and updates. Make unread chats more noticeable.
2015-09-26: Slight tweaks. Style the sticker store dialog to be readable.
2015-09-12: Tone down some whites slightly, as requested by someone.
2015-08-26: Update for conversation name in the top bar.
2015-08-16: Style the CAPTCHA dialog (yes, it exists).
2015-08-06: Update for CSS tweaks.
2015-07-23: Update for changed class names, style info at the beginning of a chat, tweak the sticker picker.
2015-06-22: Fix CSS filters on WebKit browsers. Update for new Messenger thumb-up sticker SVGs.
2015-06-03: Facebook changed the class name for link attachments.
2015-05-16: Style the sticker picker. Tweak brightness of a number of things. Fix the random scrollbar (thanks Facebook).
2015-04-13: Style audio messages and fix conversation list sidebar hiders.
2015-04-12: Make conversations with new messages more prominent. (Screenshot outdated.)