The word firestones is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 14
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (43 words)
entries, erotise, estrone, festers, finesse, fitness, foister, forests, forints, forseen, forties, fosters, infests, inserts, nesters, norites, nosiest, oftener, orients, refines, renests, resents, resifts, rosiest, seitens, seniors, sestine, sifters, sinters, snifter, softens, softies, soirees, sorties, stenose, stereos, stoners, stonier, stories, strifes, tensors, trienes, triones