Curious about you mean here. On my android phone the "search for more apps" link in the app drawer search goes to the Play Store app. Why would you want it to open a browser?
I found you can make it use Firefox by disabling the setting "Open web pages in the app".
https://gs.statcounter.com/os-market-share/mobile/worldwide/...
https://data.firefox.com/dashboard/user-activity
I love uBO, you love uBO, most of HN loves uBO, actual users either don't care enough or prefer built-ins like Brave over manual customizations and extensions. When specifically discussing mobile users who care about ad blocking also consider many prefer whole phone solutions rather than managing per app solutions, even if it means slightly worse ad blocking in certain apps.
Also remember Firefox let those specific Android users rot on the old, poor performing, and battery eating engine for 2 years longer than the desktop version. Then when they did update only some of the users who picked Firefox for extensions had support. To this day it still hasn't had basic TLC like site isolation implemented. I.e. most Android users who were willing to give Firefox a run already had a bad experience anyways, even if they did care about uBO specifically.