Depends how separate you want these.

One option is to make a second user in Mint, the OS level. This would isolate the Firefox settings for each username from each other. But this would also create separate home folders, so if you’re regularly using the same files in your personal stuff and college stuff I could see that being annoying.

Second option is to install a second browser, and just use that browser for your college account. Personal logins in Firefox, and only the college account in Chrome or whatever.