A lot of changes thanks to the feedback of the beta tester community, thanks a lot.
You can download the 5.2.1 beta installer and try the brand new Media Library and Audio Player today
Here’s the complete list of changes for 5.2.1
frostwire (5.2.1) stable; urgency=high
* Play/Pause player buttons now share the same button depending on state.
* Mac OSX threading bug when importing .m3u playlist to new playlist fixed.
* Pressing space bar pauses/resumes currently played audio.
* Playlist files can be sorted correctly by track number when available.
* FLAC playback support.
* When a playlist has finished importing files, it’s shown to the user.
* Transfer manager remembers the position of its JSplitPane.
* Transfer manager sorts downloads by default based on their creation date.
* Transfer manager has new column “Started On” showing the date the transfer
first started.
* Drag and drop issues on playlist component for Mac OSX fixed.
* Partial download dialog table can adjust column widths, a horizontal
scrollbar will appear if the sum of the columns is wider than the dialog.
* When playing an audio file, if it gets deleted FROM DISK from inside
FrostWire, the audio file will stop playing.
* Files can be dragged to the “Starred” playlist and they will be marked
as starred. If files are dragged from Disk, creating a new playlist
will be offered, and all the elements on the playlist will be starred.
* Files can be deleted from the “Starred” playlist. This will cause the
files to be unstarred on every other playlist where they belong.
* The tables on the library remember the last position of their scrollbars
during the session.
* Double clicking on a playlist name starts editing the playlist name.
* Fixes bug where downloading an individual file in a torrent wouldn’t
be marked in the search results as downloading.
* Fixes a memory leak when importing ID3 tags into a playlist.
* Fixes bug where the duration of an MP3 file wasn’t calculated correctly
by MPlayer, duration is now being calculated with Java library.
* Fixes bug where it would import torrent skipped files to iTunes.
— FrostWire Team Wed, 05 Oct 2011 13:14:11 -0500
Official FrostWire Blog 
its great!