I had to roll back my computer today because accepting the update from Opera 17 to 18 stopped "local storage" of data for at least the Rune Scape Bestiary. The page in question uses html 5 to display NPC images for the game called Rune Scape. Yes I did check the cookie settings, and they were correct for the purpose.
While the game makers (Jagex Ltd.) are focusing on making their html 5 coding work with chrome, I have found that (for now anyway) this part of the effort works more reliably in Opera 17. They are trying to make the game play in html 5 too, but as of now I can't get it to load in any browser, so Opera may be slightly ahead of the nearest competition.