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Brave browser quietly slips a VPN service onto your Windows PC
(www.androidcentral.com)
This is a most excellent place for technology news and articles.
There is Fennec available on F Droid that is basically Firefox with some blobs removed. Not as hardened as Mull but still a worthy option. There is one more browser based on Firefox called Iceraven for Android but it is not available on F Droid even. Though it supports a much wider variety of extensions than mobile Firefox does as of now. The downside is that it gets security updates usually later than Firefox, being an independent project.