refactor: one shared extension-API module, and drive the dApp flows on Firefox (closes #153)

tests/e2e/network.js

@@ -93,6 +93,13 @@ function word(value) {
 // is put there by the shipped manifest's MAIN-world content script, exactly
 // as it is on any http(s) page a user visits, so what these tests speak to
 // is the real inpage provider and not a copy the harness wired up.
+//
+// DAPP_HTML below is exported and served verbatim by the Firefox suite too
+// (tests/e2e/firefox/dapp.js), from a loopback origin rather than through a
+// route handler. The two suites drive different browsers over different
+// protocols, but the page they drive — the __dapp API, the message log — is
+// one fixture, so an assertion written against it means the same thing on
+// both.
 const DAPP_ORIGIN = "https://dapp.e2e.test";
 const DAPP_URL = DAPP_ORIGIN + "/";
 
@@ -686,6 +693,7 @@ async function installNetworkStubs(ctx, opts) {
 
 module.exports = {
     installNetworkStubs,
+    DAPP_HTML,
     DAPP_ORIGIN,
     DAPP_URL,
     FEE_ESTIMATE_WEI,