Facebook said in a post on its developer blog:
FBML apps will no longer work on platform. The “FBML Removal” migration now appears and is enabled for all apps. It will be possible to disable the migration, thereby re-enabling FBML, until July 5, 2012, when the migration and all FBML endpoints will be removed completely.
Facebook originally announced its intentions to begin phasing out FBML in favor of iFrames in early 2011, and the process has been gradual, with the last communication on the topic coming in the form of this announcement late last December:
FBML will no longer be supported as of Jan. 1, 2012. Aside from security- and privacy-related bugs, we will not fix any bugs related to FBML after Jan. 1, 2012. On June 1, 2012, FBML endpoints will be removed from platform.
June 1 apparently became July 5 at some point in the past few months, but the message remains the same: FBML holdouts’ time with their loved one is short.