In the coming months Mozilla will launch support for an open ecosystem of extensions on Firefox for Android on addons.mozilla.org (AMO). We’ll announce a definite ...
Yep, after I found this out I ditched Chrome immediately once they started rolling out Google Search ads that couldn't be blocked via DNS. Firefox mobile feels a little less smooth than Chrome admittedly, but the ability to add extensions like ublock/darkreader/consent-o-matic make is a no contest in terms of overall user experience.
The one knock is that they took bypass paywalls out of their extension store and the workaround to install it is somewhat cumbersome, so now I'm annoyingly using Kiwi browser for paywalled content and Firefox for everything else. Hopefully this update will make it so I only need one browser again.
Then to add your custom collection in mull (or ff nightly, I guess) enable debug mode by going to settings > about mull and tapping the logo 5 times. Then go back and under the advanced section you can find "custom add-on collection"