Bug 1825061 - Fix Hulu caption observer. r=pip-reviewers,mhowell

    if (container) {

      updateCaptionsFunction("");

      const callback = function(mutationsList, observer) {

        let text = container.innerText;

        updateCaptionsFunction(text);

        // This will get the subtitles for both live and regular playback videos

        // and combine them to display. liveVideoText should be an empty string

        // when the video is regular playback and vice versa. If both

        // liveVideoText and regularVideoText are non empty strings, which

        // doesn't seem to be the case, they will both show.

        let liveVideoText = Array.from(

          container.querySelectorAll(

            "#inband-closed-caption > div > div > div"

          ),

          x => x.textContent.trim()

        )

          .filter(String)

          .join("\n");

        let regularVideoText = container.querySelector(".CaptionBox").innerText;

        updateCaptionsFunction(liveVideoText + regularVideoText);

      };

      // immediately invoke the callback function to add subtitles to the PiP window