[java] can't modify an unmodifiable map

Author: titusfortner

java/src/org/openqa/selenium/remote/session/FirefoxFilter.java

@@ -55,6 +55,8 @@ public Map<String, Object> apply(Map<String, Object> unmodifiedCaps) {
     Map<String, Object> options = (Map<String, Object>) unmodifiedCaps.getOrDefault(
       "moz:firefoxOptions",
       new TreeMap<>());
+    options = new TreeMap<>(options);
+
     if (unmodifiedCaps.containsKey("firefox_binary") && !options.containsKey("binary")) {
       // Here's hoping that the binary is just a string. It should be as FirefoxBinary.toJson just
       // encodes the path.