animations_inspector_events.js

async onAnimationsMutation(changes) {
  if (!this.isPanelVisible()) {
    return;
  }
  // ...
}

async onTargetAvailable({ isTopLevel, targetFront }) {
  if (isTopLevel) {
    this.animationsFront = await targetFront.getFront("animations");
    this.animationsFront.setWalkerActor(this.inspector.walker);

    this.animationsFront.on("mutations", this.onAnimationsMutation);
  }
}

async initListeners() {
  await this.inspector.toolbox.targetList.watchTargets(
    [this.inspector.toolbox.targetList.TYPES.FRAME],
    this.onTargetAvailable
  );

  this.inspector.sidebar.on("select", this.onSidebarSelectionChanged);
  // ... attach all the listeners ...
  this.inspector.toolbox.on("select", this.onSidebarSelectionChanged);
  // Call onSidebarSelectionChanged because we might have missed the initial
  // "select" events while waiting for the target
  this.onSidebarSelectionChanged();
}