diff --git a/index.html b/index.html
index 015397f..c030ca6 100644
--- a/index.html
+++ b/index.html
@@ -128,12 +128,18 @@
     }
 
     class Base64NumeralSystemInput extends NumeralSystemInput {
-        static defaultAlphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
-        static dropdownOptions = {"Standard": ['+', '/'], "Filename": ['-', '_'], "IMAP": ['+', ',']};
+        // TODO Convert static methods to static properties once supported by Firefox
+        static defaultAlphabet() {
+            return "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+        }
+
+        static dropdownOptions() {
+            return {"Standard": ['+', '/'], "Filename": ['-', '_'], "IMAP": ['+', ',']};
+        }
 
 
         constructor(name) {
-            super(name, new NumeralSystem(64, Base64NumeralSystemInput.defaultAlphabet, true));
+            super(name, new NumeralSystem(64, Base64NumeralSystemInput.defaultAlphabet(), true));
 
             this.dropdownLabel = document.createElement("label");
             this.dropdownLabel.setAttribute("for", `${this.name}Dropdown`);
@@ -143,7 +149,7 @@
             this.dropdown = document.createElement("select");
             this.dropdown.id = `${this.name}Dropdown`;
             this.dropdown.onchange = () => {
-                const selectedOption = Base64NumeralSystemInput.dropdownOptions[this.dropdown.value];
+                const selectedOption = Base64NumeralSystemInput.dropdownOptions()[this.dropdown.value];
                 this.setLastDigits(selectedOption[0], selectedOption[1]);
             };