I wouldn't recommend Slime to ANYONE because the developers do not care about security. The issue[0] of a gaping security hole has been open for going on two years.
https://github.com/slime/slime/issues/286
If it has being left unaddressed because no one thinks it is enough of a problem. That is how free software works
Tl;dr: web sites can send requests to localhost TCP sockets despite origin restrictions using a trick called DNS rebinding.