Very good addon, thanks.
Can you add those features below?
 Add a context menu "Add to Selection Context Search" when we right-click inside a search form.
 Improve the management of the search engine list. Now, if we have a lot of search engines and need to change the row position of one search engine far below on the list, we need scroll all the way down, select the search engine, then scroll all the way up, then click "move up" to change the row position. With few search engines, that is ok, but with a huge amount, that is not good.
# Answer 01 - 2017.09.03
An example? Right here, on AMO. With the "Selection Search"  extension for Google Chrome, if I Ctrl+Alt+Click the search form a popup appears .
I like the drag-and-drop method  used by the "Selection Search" extension, it really is very easy to manage this way.
My list right now has 32 search engines, the less used ones are hidden inside folders.