How do i switch back to regular mail?

I tried switching to mail beta and i cant even log in.. after i enter my pword, it goes to a loading page and then i get an error. it is a runtime error. string: 3403 error: Unterminated string constant. And it asked me to debug. then a windows pop up appears and states that Yahoo! Mail experienced a login error: Login error: Error expected. I cant even check my mail let alone switch back.