Switch back to Firefox UA for Google Account quirk

Looks like the Edge one doesn't work anymore.

Reverts db13e52 and reintroduces the Firefox UA
removed in e010afd (but updated).

Closes qutebrowser#5182.

qutebrowser/browser/webengine/webenginesettings.py

@@ -431,11 +431,7 @@ def _init_site_specific_quirks():
                      "AppleWebKit/537.36 (KHTML, like Gecko) "
                      "Chrome/99 "
                      "Safari/537.36")
-    edge_ua = ("Mozilla/5.0 ({os_info}) "
-               "AppleWebKit/{webkit_version} (KHTML, like Gecko) "
-               "{upstream_browser_key}/{upstream_browser_version} "
-               "Safari/{webkit_version} "
-               "Edg/{upstream_browser_version}")
+    firefox_ua = "Mozilla/5.0 ({os_info}; rv:90.0) Gecko/20100101 Firefox/90.0"
 
     user_agents = [
         # Needed to avoid a ""WhatsApp works with Google Chrome 36+" error
@@ -447,7 +443,7 @@ def _init_site_specific_quirks():
         # Needed to avoid a "you're using a browser [...] that doesn't allow us
         # to keep your account secure" error.
         # https://github.com/qutebrowser/qutebrowser/issues/5182
-        ("ua-google", 'https://accounts.google.com/*', edge_ua),
+        ("ua-google", 'https://accounts.google.com/*', firefox_ua),
 
         # Needed because Slack adds an error which prevents using it relatively
         # aggressively, despite things actually working fine.