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Firefox to become first mobile browser to support desktop extensions later this year
(blog.mozilla.org)
This is a most excellent place for technology news and articles.
How do I make use of this? I can't see a way to install them on my Fennec from F Droid
You have to add a custom addons collection. That's how.
I haven't gotten around making them and using them, and it seems every guide online is vastly out of date