To make the toolbar button work on Apple's Safari web browser:
Change the "document.getSelection()" part of the URL in mE123's instructions to "getSelection()" instead.

i.e. the URL becomes:
"javascript:Qr=getSelection();if(!Qr){void(Qr=prompt('Enter what you want to find on Everything:',''))}if(Qr)location.href='http://www.everything2.com/index.pl?node='+escape(Qr)+' '"