EDIT:
For the sake of simplicity:
I’ve got a simple UserJS script (FF/Chrome: Greasemonkey, Opera: built-in) that fixes some issues on website I’m using quite often. The problem is that I need to store some data between different requests. My first attempt was LocalStorage but it fail when it came to work with subdomains: www.domain.com and subdomain.domain.com (unfortunately root-domain is subdomain in fact – stupid www) . I need to be able to access some data source that would be available everywhere.
Now I’m stuck – any ideas?
…Why not use GM_setValue and GM_getValue?
EDIT: I did a little digging. Look what I found!
http://www.opera.com/docs/userjs/specs/#scriptstorage
It claims to work the same as localStorage, but it’s scoped per-script, rather than per-website. Should work perfect for your use case.