Actually, it's not possible to choose what action to perform. After selection, nothing is displayed and it always opens new tabs. Also, multilinks had the ability to do multiple selections in a row. SLP ends the selection right after the mouse button is released. Too bad.
For now, the best solution for me is to stick with FF 56.0.2 and legacy versions of my favourite extensions.
TO USER: Best of I used!! already: custom key to hold TBC : delay in opening! delay in opening! delay in opening! waiting so long~~~ source: [Feature Request: Optional Delay For Opening Each New Tab · Issue #114 · cpriest/SnapLinksPlus](https://github.com/cpriest/SnapLinksPlus/issues/114)