In the following spots a "MouseUp" eventName is being used, which does look inconsistent considering that the "Mouse Down"/"Mouse Enter"/"Mouse Exit" eventNames all have a space in them.
Is this inconsistency actually expected, or is it a simple typo? If the former, then a comment explaining *why* would be appropriate; otherwise we should just fix this :-)

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L806

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L945

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1034

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1168

/cc @calixteman 
const name = event.target.name;
      for (const checkbox of document.getElementsByName(name)) {
        if (checkbox !== event.target) {
          checkbox.checked = false;
          storage.setValue(
            checkbox.parentNode.getAttribute("data-annotation-id"),
            { value: false }
          );
        }
      }
      storage.setValue(id, { value: event.target.checked });
    });
    if (this.enableScripting && this.hasJSActions) {
      element.addEventListener("updatefromsandbox", event => {
        const { detail } = event;
        const actions = {
          value() {
            event.target.checked = detail.value !== "Off";
            storage.setValue(id, { value: event.target.checked });
          },
          focus() {
            setTimeout(() => event.target.focus({ preventScroll: false }), 0);
          },
          hidden() {
            event.target.style.visibility = detail.hidden
              ? "hidden"
              : "visible";
            storage.setValue(id, { hidden: detail.hidden });
          },
          editable() {