How to install browser extensions (like Adblock or Metamask)?

With the exception of 3D WebView for Android with Gecko Engine (mentioned below), 3D WebView doesn't support WebExtensions, so it's unable to use existing browser extensions like Adblock or Metamask out-of-the-box. This is because most of the browser engine libraries used internally by 3D WebView don't support WebExtensions. However, an application can still implement extension-like functionality using the following 3D WebView APIs:

Browser extensions for Android Gecko

3D WebView for Android with Gecko Engine is the only 3D WebView package that supports WebExtensions, which can be installed with AndroidGeckoWebView.EnsureBuiltInExtension(). Please note that WebExtension API support varies from browser to browser, so if an extension hasn't explicitly been tested to work with mobile Gecko, then it may not function correctly.