WordPress 3.9 Beta 1  has been released!
- We updated TinyMCE, the software powering the visual editor, to the latest version. Be on the lookout for cleaner markup. Also try the new paste handling — if you paste in a block of text from Microsoft Word, for example, it will no longer come out terrible. (The “Paste from Word” button you probably never noticed has been removed.) It’s possible some plugins that added stuff to the visual editor (like a new toolbar button) no longer work, so we’d like to hear about them (#24067 ). (And be sure to open a support thread  for the plugin author.)
- We’ve added widget management to live previews (the customizer). Please test editing, adding, and rearranging widgets! (#27112 ) We’ve also added the ability to upload, crop, and manage header images, without needing to leave the preview. (#21785 )
- We brought 3.8?s beautiful new theme browsing experience to the theme installer. Check it out! (#27055 )
- Galleries now receive a live preview in the editor. Upload some photos and insert a gallery to see this in action. (#26959 )
- You can now drag-and-drop images directly onto the editor to upload them. It can be a bit finicky, so try it and help us work out the kinks. (#19845 )
- Some things got improved around editing images. It’s a lot easier to make changes to an image after you insert it into a post (#24409 ) and you no longer get kicked to a new window when you need to crop or rotate an image (#21811 ).
- New audio/video playlists. Upload a few audio or video files to test these. (#26631 )
Developer Related Changes
- The load process in multisite got rewritten. If you notice any issues with your network, see #27003 .
- We now use the MySQL Improved (mysqli) database extension if you’re running a recent version of PHP (#21663 ). Please test your plugins and see that everything works well, and please make sure you’re not calling
- Autosave was refactored, so if you see any issues related to autosaving, heartbeat, etc., let us know (#25272 ).
- Library updates, in particular Backbone 1.1 and Underscore 1.6 (#26799 ). Also Masonry 3 (#25351 ), PHPMailer (#25560 ), Plupload (#25663 ), and TinyMCE (#24067 ).
- TinyMCE 4.0 is a major update. Please see TinyMCE’s upgrade guide  and our implementation ticket  for more. If you have any questions or problems, please open a thread in the support forums .
Download: WordPress 3.9 Beta 1