"Subscribe to this feed" button in Opera adds feed to the internal feed aggregator. It may be changed: clicking on this button results in HTTP request to the URL mentioned in the <link> tag, and it is possible to rewrite this URL to the URL adding current RSS feed to tt-rss.
To achieve this, place this script to your Opera UserJS directory (Tools->Preferences->Advanced->Content->Java Script options->User Java Script files...), changing installation_root to the base URL of your tt-rss installation, and default_category to the category you want to add subscribed feeds (0 is uncategorized category).
Having done this, try to load some page with has feeds declared in <link> and click the feed button. Nothing visible should happen (no 'Wanna subscribe?' dialog from built-in aggregator should pop pu). You should now have feed added to tt-rss. If not, check whether you are logged in to your tt-rss.
