Has anyone noticed women with muscle, mostly on webcam wearing corsets? Is it to keep their abs tight? Or are they just cold? :-)

I think it is because corsets became part of fetish gear. Their historical roots were from European clothing in which women used to make their waist seem smaller. When it fell out of use then it came into underground fetish culture in erotic related materials. It could be that Fbbs use the corset to make their upper body look larger by making the waist look smaller . I can't confirm this, it is more of a theory.

It was stylish for women before 20th century ,to  emphasize tiny waist
but was quite a torture : organs were compressed.breating was blocked

unimaginable ,for perforning a fit ,healthy life ,so better training-add mass on chest,shoulders  and  pelvis ,together with situps,,,same effect !!

I sessioned with one pro known for her X frame who mentioned she uses one. Google "bodybuilding corset" and you'll find plenty of information about it. They're also called waist trainers and are used to compress the waist with the goal of reducing it beyond its natural, lower limit, and need to be worn for extended periods to do so. From what I've read, they do work and are used by a lot of bodybuilders, both male and female, but do have the potential health consequences you'd expect.