Is it possible to set a cookie from a browser plug-in?

Question

Do browser plug-ins, such as the Yahoo toolbar or others, have the ability to set cookies on multiple domains as the user browses the web? Does the browser expose the necessary access to do this to a plug-in? If this varies across browsers, that would be helpful to know as well.

Thanks!

Answer 1

• Cookies are stored in files and real plugins (i.e. ones using NPAPI rather than the browser's addon/extension engine) can read/write files. Hence, it's possible to do for any browser this way, although not really straightforward.
• Firefox exposes cookies even to addons since there are cookie editor addons (that can edit cookie for any site).
• Chrome/Chromium allows setting of cookies through "content scripts" that run in the context of a page (any page) - that's only in the beta branch so far, but soon to be in stable. However, the downside is that you might have to visit the site for it to work (you could fake that using iframes).
• No idea about Opera.