How do I create a new profile without opening firefox?

Firefox is not opening for me even after I uninstalled and re installed it, I have been told that often this problem can be fixed by resetting my fire fox account, and while I have been instructed on how to access my profile without opening fire fox there is nothing that will tell me how to reset my profile or create a new profile without opening fire fox. Please help, I don't want to loose my important information and I really really don't want to use chrome... it sucks...

Thank you