Kiwi browser is basically chrome but with full extension/dev tools support. Nothing custom, all stock chrome. But I know the devs behind that browser rely on data collection themselves, so it's less than ideal (you can I think turn all of that off but I'm not sure). But it shows that it is possible to have full add-on support on mobile chromium. Especially considering Kiwi was developed by a single dev initially.

Most open source chromium forks on Android don't have add-ons though, so kiwi is the best option. I guess it's usually because those forks are usually very privacy centric so add-on support is far from a priority. Kiwi on the other hand is basically stock desktop chrome

Edit: apparently they don't outright collect user data!

>The browser is getting paid by search engines for every search done using Kiwi Browser.

>Depending on the search engine choice, requests may go via Kiwibrowser / Kiwisearchservices servers. This is for invoicing our search partners and provide alternative search results (e.g. bangs aka "shortcuts").

>In some countries, the browser displays sponsored tiles or news on the homepage.

>User data (browsing, navigation, passwords, accounts) is not collected because we have no interest to know what you do in the browser. Our main goal is to convince you to use a search engine partner, and this search engine makes money / new partnerships and shares revenue with us.

No, so even though Firefox barely has any, it's still more than Chrome.