The tv-auto-open-on-import variable controls whether the tm-import-tiddlers message causes the tiddler $:/Import (which lists the pending imports) to open in the story river.

By default, the tiddler is opened. But if this variable has the value no, it isn't.

An example of setting this variable to no can be found in the upgrade plugin within the TiddlyWiki Upgrade Wizard. People can drag their wiki files onto the wizard without triggering the normal import display.