This add-on (Audio Equalizer) prevents playback of any video thumbnail that doesn't have audio especially in less popular websites. This can be easily ascertained by simply disabling the add-on (Audio Equalizer) and seeing the problem disappear.

While in private mode with nothing but this add-on (Audio Equalizer) enabled and after the page is fully loaded. Bringing the cursor/touch pointer to a standstill over an 'image' thumbnail will trigger the fetching and playback of 'video' thumbnail.

Afterwards in the developer console (F12) we see the following warning (Yellow Background) generated immediately:

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An AudioContext was prevented from starting automatically. It must be created or resumed after a user gesture on the page.
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I would like to point out that I have had already changed the Autoplay permission in Firefox's privacy setting page (about:preferences#privacy) for all websites from 'Block Audio' to 'Allow Audio and Video' Before Installing this add-on (Audio Equalizer).

Above warning is then immediately followed by the error (Red Background) below:

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Uncaught (in promise) DOMException: The fetching process for the media resource was aborted by the user agent at the user's request. inject.js:97

attach moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js:97
attach moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js:86
moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js:135
EventListener.handleEvent* moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js:133

attach moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js:97
forEach self-hosted:160
attach moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js:86
moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js:135
(Async: EventListener.handleEvent)
moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js:133
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I tried to use the ON/OFF button in the add-on (Audio Equalizer) from its own popup so that the add-on (Audio Equalizer) remains enabled in Firefox but doesn't try to inject the following script which is the source of error ( into the page:

moz-extension://[ADDON-UUID]/data/content_script/page_context/inject.js

However probably thanks to Audio Equalizer's 'Access your data for all websites' permission, Unless you disable the add-on (Audio Equalizer) from inside the Firefox's add-on page (about:addons) the script will still get injected and thus no video thumbnail playback.

I even tried adding 'moz-extension://[ADDON-UUID]' to uBlock Origin's "My filters" and "My rules" tabs based on each tab's correct syntax while removing 'moz-extension-scheme' from "Trusted sites", nevertheless Firefox would still inject the script into the website so long as the add-on was enabled despite "ON/OFF" button being gray (presumably indicating an 'off' state) rather than black (presumably indicating an 'on' state) according to its own popup menu.

As it's not properly programmed to handle audio-less videos and there is no way included to prevent itself from activating on user-defined specified websites (say by actually having an options tab that comes with a configurable exclusion list inside add-on's Firefox page rather than its popup with its ineffective "ON/OFF" button); I believe that the badge granted to this add-on by Mozilla Foundation is without merit and should be revoked.

After all the following is a direct quote from hovering over the badge of each add-on recommended by Mozilla Foundation:
"Firefox only recommends extensions that meet our standards for security and performance"