To make room for Florence, the Lions placed safety Amari Spievey on injured reserve. Spievey hasn't played since suffering another concussion, and as Dave Birkett tweeted, he is now in "Jahvid Best territory." Spievey dealt with the effects of a concussion he suffered against the New Orleans Saints in the playoffs all the way into the summer, and he's now had four concussions in his life. Unfortunately, this could be another situation where Spievey may not be able to play for some time or at all.
As for Florence, he is returning after breaking his forearm back in Week 2 against the San Francisco 49ers. The Lions placed him on IR with the designation that he would return later in the season. Florence was practicing with the Lions the last couple weeks, and now he is back on the roster and ready to play on Sunday.