Your browser history will be full of URLs that only your browser can access. A contributor was kind enough to build a delete function for this to wipe the private key and generate a new one. This would render all those URL's useless. We'll be merging that soon.

Sort of. Malicious browser extensions could look at history and look at local storage before the key is deleted.

A malicious browser extension can steal all sorts of secrets. Is there a unique weakness here in the linked tool? Otherwise, this seems similarly vulnerable to everything else on the web.