How to add a Safari toolbar button that runs an AppleScript
Another solution, and this is really dependant on what you want to do, is to use Services to execute your Applescript.

It doesn't create a toolbar icon, but will allow you to create a service from your AppleScript. You can then define a shortcut key in the System Preferences Keyboard Services pane

This page over at automatedworkflows.com shows an example as well as a link to the rather useful ThisService program.