'Toggle Mixed Display Content' runs flawlessly but together with its sister add-on 'Toggle Mixed Active Content' could be slightly enhanced with the following :
The toolbar's button tool-tip mentions "content blocked"/"content not blocked" when it could preferably precise the content by stating "active" for the 'Toggle Mixed Active Content' add-on and "display" (or "passive") for the 'Toggle Mixed Display Content' add-on.
Rather a cherry suggestion when the cake is just fine.
Together with Toggle Mixed Active Content, it makes my life easier. I only hope for a whitelist. ScienceDirect (a website for Elsevier journals) is totally broken with the content blocker, you have to grant permission in each page reload (try looking for an article). An extension with the capability of remembering which websites I rely on would be very well received.