Update Firefox binary startup artifacts to 3.0.0b2

As mentioned in #260, this is not the best way to manage webdriver
updates, as it necessitates a new Perl release in tandem with the
webdriver releases, and I am not nearly up to date.

However, in lieu of a better long term solution, this kludge is all
we've got.

lib/Selenium/Firefox/webdriver_prefs.json

@@ -40,15 +40,6 @@
     "security.csp.enable": false,
     "security.fileuri.origin_policy": 3,
     "security.fileuri.strict_origin_policy": false,
-    "security.warn_entering_secure": false,
-    "security.warn_entering_secure.show_once": false,
-    "security.warn_entering_weak": false,
-    "security.warn_entering_weak.show_once": false,
-    "security.warn_leaving_secure": false,
-    "security.warn_leaving_secure.show_once": false,
-    "security.warn_submit_insecure": false,
-    "security.warn_viewing_mixed": false,
-    "security.warn_viewing_mixed.show_once": false,
     "signon.rememberSignons": false,
     "toolkit.networkmanager.disable": true,
     "toolkit.telemetry.prompted": 2,
@@ -64,12 +55,12 @@
     "browser.newtabpage.enabled": false,
     "browser.startup.page": 0,
     "browser.startup.homepage": "about:blank",
+    "browser.startup.homepage_override.mstone": "ignore",
     "browser.usedOnWindows10.introURL": "about:blank",
     "dom.max_chrome_script_run_time": 30,
     "dom.max_script_run_time": 30,
     "dom.report_all_js_exceptions": true,
     "javascript.options.showInConsole": true,
-    "network.http.max-connections-per-server": 10,
     "startup.homepage_welcome_url": "about:blank",
     "startup.homepage_welcome_url.additional": "about:blank",
     "webdriver_accept_untrusted_certs": true,