It'd be funny if there's a global state shared with everyone who has the button stealer extension installed: so if I stole a button, it'd be missing when you visit the page.
It would leave behind an outline of the button, and if you needed to use it you'd have to put up the strongest button from your stash to try to defeat the stolen button in combat. If you weaken the button enough, you can throw a button capsule at it to capture it.