Clicking on the the Active App icon (or pressing ⌘P on the keyboard) will toggle Active Application filtering mode.
When enabled, the name of the current application will display at the title of Trickster’s window. The active app icon is also always displayed in that location pointed by the arrow. When active, only files that Trickster thinks are relevant to currently active application will show.
When Trickster processes files, it notices which app was the active one (its name displayed in the menu bar) when that files was processed.
When the current application filter is on, Trickster will display files that either were processed when the current application was active or files that can be opened by it. Thus, for some application, which mark that they can accept any kind of file, the filter will still display all files.
This filter works in addition to any other active filters you have, like a sidebar filter or text in the search field.