She doesn't cut loose anymore because of some PIS involving her becoming sterile if she uses her power too much or some such. She has motherly aspirations ya know... Or had.
But at her peak she was able to instantly grab all of the microwave energy available from the atmosphere or Earth and channel it into blasts. In vacuum with unfiltered microwaves she was even more powerful.
Originally posted by Oliver North
like I said in the FS vs Mags thread, my only real familiarity with her is Maximum Carnage, where she wasn't close to that powerful
Keep in mind this was during the 90s. It could have changed. That's the version of Firestar I'm referring to.