diff --git a/grafanimate/marionette.py b/grafanimate/marionette.py
index 78dc5ef..d3239a3 100644
--- a/grafanimate/marionette.py
+++ b/grafanimate/marionette.py
@@ -110,10 +110,11 @@ def configure_marionette(self):
 
     @classmethod
     def find_firefox(cls):
-        candidates = [
+        candidates = []
+        candidates += where.where("firefox-bin") + where.where("firefox-esr")
+        candidates += [
             os.environ.get("FIREFOX_BIN"),
-            where.where("firefox-bin"),
-            where.where("firefox-esr"),
+            "/Applications/Firefox.app/Contents/MacOS/firefox",
             "/Applications/Firefox.app/Contents/MacOS/firefox-bin",
         ]
         firefox = find_program_candidate(candidates)
diff --git a/grafanimate/util.py b/grafanimate/util.py
index 806b055..ebe25ed 100644
--- a/grafanimate/util.py
+++ b/grafanimate/util.py
@@ -43,6 +43,8 @@ def read_list(data, separator=","):
 
 def find_program_candidate(candidates):
     for candidate in candidates:
+        if candidate is None:
+            continue
         if os.path.isfile(candidate):
             return candidate