Simply visit pwa.kiwix.org in Firefox on Android. Read more after the demo:
(be patient while the demo loads)
See also: [ Install PWA and use OPFS in Chrome for Android ] [ Demo of all OPFS features ]
Firefox supports installing PWAs on Android (but not on Desktop). This is worthwhile because the app runs in its own dedicated session and has its own icon in your Home Screen.
As shown in the Demo, Firefox for Android works best when using the Origin Private File System. Loading larger archives from the user-visible File System can be slow and glitchy on Firefox for Android, because the browser attempts to load the whole file into memory. So you are generally limited to files that will fit in the OPFS.
Firefox currently limits the maximum size of the OPFS to ~10GB. On Chromium browsers, there is usually a much larger quota (limited only by the amount of free space in your storage).
See also: [ Install PWA and use OPFS in Chrome for Android ] [ Demo of all OPFS features ]