I don't think that there is anyway I would sign up for something that would allow people to cancel my upvotes. Even if I did, I'd open another browser to upvote

I don't think that there is anyway I would sign up for something that would allow people to cancel my upvotes. Even if I did, I'd open another browser to upvote and only us the extension enabled one to downvote, which would negate the point of the system. I don't think that it would work.