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Firefox will support at least 200 new extensions on Android this December
(www.androidpolice.com)
This is a most excellent place for technology news and articles.
For anyone who is unaware, Firefox developer edition on mobile, otherwise known as Firefox nightly, never lost the ability to arbitrarily install extensions. You just need to make your own collection on the Firefox website, and link it in the settings on your phone.
There are also Firefox forks, but you have to install apk manually and then extension are easy to download without developer collection
Fireforks