Opera “Search with”

What Opera version are you using? According to this thread, searching using the context menu always opens in a new tab - which is the behavior I am seeing with 10.51, regardless of whether "Reuse current tab" is checked in Preferences -> Advanced -> Tabs (although it does affect searching from the search box).

This functionality doesn't exist yet in Opera Blink (currently on version 19). Remember, Opera went through a major change from Presto (12.x) to Blink (15+), and they're trying to gradually get all that functionality back bit by bit in each new release.

Additionally, there is always the danger that such functionality can be hi-jacked by malware - which is why this functionality was removed in a security fix from Opera 12.14 to 12.15 and wasn't added back in in the latest Presto version, 12.16.

From the Opera 12.15 release notes:

Fixed an issue where the search bar's default engine could be overridden by third-party apps.

So please don't assume it's an "arbitrary restriction" just because you don't like it. ;-) Also, not too long ago, Opera was the only browser allowing you to even have custom search engines. If you're happy to live with that little security hole due to confidence in your firewall/virus scanner, use 12.14 (you can use that alongside Opera Blink and even right-click on a webpage and "open with" Blink or any other browser); otherwise, you'll have to wait until this gets added back to Opera Blink, or until your favourite search engine gets added to the list of "standard" ones. You can always post to the Desktop wish-list forum.