FOCUS Enhancements 3.2 - Manual (Page 48)

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Figure 8. Media Review Page (Deleting Multiple Files)
WARNING
You may delete any or all media files from the Firefly in this fashion.
This includes files that may be in use by the current playlist. If you
delete a file that is currently playing, it will be allowed to finish
playing before the file is actually removed. The next time it is called
by the playlist it will be skipped.
There is no way to recover files after they have been deleted.