[chmod775]

One should really avoid installing a bunch of random extension with read/write permissions to every page. Both of these extensions have ~quivalents within firefox' settings:

    media.autoplay.*
    dom.event.contextmenu.enabled

Firefox also allows you to manage autoplay permissions on a per-page basis via regular settings (I believe it also shows via a setting on the URL bar if firefox blocked autoplay).

Also Shift+RMB will bypass any contextmenu blocking even when it's enabled by default.

If you want to fix unselectable text, you could also use the adblocker you already have to achieve that. For example using these rules:

    *##+js(acis, disableSelection, reEnable)
    *##+js(acis, document.oncontextmenu)
    *##+js(aopr, document.ondragstart)
    *##*:style(-webkit-touch-callout: default !important; -webkit-user-select: text !important; -moz-user-select: text !important; -ms-user-select: text !important; user-select: text !important;)