How do you bring up the effects settings window? Rank beginner with fcpx here. I keep having trouble using the effects. Sometimes I move my cursor into the little window for a given effect, and I can scrub back and forth, and sometimes I can edit the parameters of the effect, but it seems I can never do both.

As a concrete example, in this screenshot, I've moved my cursor into the "censor" effect which pixelates a circle in the center of the picture.

When I did this previously, the circle of pixelation had handles on it so I could drag it and resize it, and the inspector had a number of settings I could change.

Now I'm in a state where I can't preview the effect, the inspector isn't showing the settings, and more often than not, double-clicking the effect has no effect.

Is there some sort of mode switch or setting I'm missing?
By scrubbing the thumbnail you're only previewing the effect. To add it to the clip, drag the thumbnail to the clip on the timeline in your project. The effect is then added to the effects in the thumbnail (at the top of your screenshot) and controls are available in the inspector and the viewer for manipulating the effect.