She has also competed in 10K competitions and was the 2008 winner of the Casablanca Women's Run. She made her marathon debut that year at the Košice Peace Marathon and managed to finish as runner-up on her first attempt. She received a late-minute invitation to run the Rome City Marathon in March 2009 and went on to surprise the field by winning the race in a time of 2:27:08 hours – over ten minutes faster than her previous best. Her second race over the distance that year came at the Frankfurt Marathon, where she again finished under two and a half hours to take fourth place. Firehiwot won the Boulogne-Billancourt Half Marathon in November with a course record time of 1:09:26 – the first time a woman had run under an hour and ten minutes at the race.
Firehiwot took an unprecedented third straight title in Rome in 2011 and knocked over a minute off her best in the process, completing the race in 2:24:13 hours. She established herself among the world's foremost women marathon runners with a victory at the 2011 New York City Marathon, where she held off Buzunesh Deba and Mary Keitany to win in a time of 2:23:15 hours. She opened her 2012 season with a course record win at the New York City Half Marathon, where she maintained a fast starting pace to hold off Kimberley Smith and set a new best of 1:08:35 hours. The 2012 Boston Marathon was undertaken in warm conditions and she managed fourth place behind a Kenyan trio.