Sometimes widget replacement fails (#2331, #1542 (comment)), and sometimes it succeeds but our placeholder is unusable for some reason (Spotify, SoundCloud on Tumblr (#787), #2281).

When replacement fails for a blocked widget that provides/is required for desired functionality, it's not clear why a video is missing, a form that requires reCAPTCHA doesn't work, etc. as Privacy Badger doesn't show anything inside the page, nor anything specifically about video players or CAPTCHA providers in the popup.

When replacement succeeds but clicking our placeholder doesn't do anything, there is no obvious way to activate it in another way.

We should add UI to the popup to show the widgets that should have been replaced on the current page. This should help make it clear what Privacy Badger meant to replace. This will also allow users to activate each widget regardless of whether its replacement is present and usable.