opera search bar: enter doesn't search
My solution for SO uses an undocumented feature (an easy trick when there's no documentation whatsoever): longtouch the search bar, add it as a search engine, and then use Opera's own search bar for such sites.  A trick you may like with SO is to do this multiple times, then manage search engines, click on one of the SO 'engines', and modify it so that you can readily add e.g. [android] to your searches.  It may feel like a workaround, but the result is more comfortable than what I was used to on desktop systems.