Currently tab selector receives thumbnails with screen-shots of the site in general, not a snap-shot of what is actually opened in the tab. This might be too coarse, especially for ajax sites. When user has opened 2 tabs of Google Maps one with entire globe and one with New York close-up, he may expect thumbnails to reflect it. The adjustable thumb-nail size could be a plus to, so that other clients could request smaller (or bigger) thumbnails. This bug is filled up as a follow-up of a small discussion. I don't think it should receive any serious priority.
should be implemented downstream in a browser code