since long time we used "FlashBlock" on Firefox, but there is another tool call "Stop Autoplay",
with "Stop Autoplay" there are more options more than FlashBlock and smaller in size even and look like nice,
you can see the difference in both photo for both tools


and I think good idea to replace "FlashBlock" by "Stop Autoplay" in final Porteus.
almost,
FlashBlock = 82 KB
Stop Autoplay = 41 KB
https://addons.mozilla.org/en-US/firefo ... -autoplay/

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Never install Stop Autoplay together with Flashblock, only one of both add-ons will work for you!
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Best Regards.