Perlmonks specific? Not exactly.
Cookies specific? Yes.
Browser specific? To the extent that JS is.

JS, as you may or may not know, can read cookies. Cookies generally are safe from prying eyes because they can only be sent back to the originating domain, in this case perlmonks.org. However, the JS on home nodes comes from the same domain and therefore has access to all cookies set anywhere else on perlmonks.org. That includes your username/password cookie. An unscrupulous user can insert JS code that, for instance, grabs that cookie and /msgs or e-mails it to him. He could then set that cookie in his own browser, thus logging in as you, and post / chat / change settings or passwords with your permissions, and, to the automated parts of the site, indistinguishably from you.

This is obviously a security risk. There has been much discussion about it before. Currently the only known way to prevent this is to turn off client-side scripting.