--- a/dom/chrome-webidl/PrioEncoder.webidl
+++ b/dom/chrome-webidl/PrioEncoder.webidl
@@ -6,17 +6,15 @@
 
 [ChromeOnly, Exposed=Window]
 namespace PrioEncoder {
   [Throws, NewObject]
   PrioEncodedData encode(ByteString batchID, PrioParams params);
 };
 
 dictionary PrioParams {
-  required boolean browserIsUserDefault;
-  required boolean newTabPageEnabled;
-  required boolean pdfViewerUsed;
+  required sequence<boolean> booleans;
 };
 
 dictionary PrioEncodedData {
   Uint8Array a;
   Uint8Array b;
 };
\ No newline at end of file

--- a/dom/prio/PrioEncoder.cpp
+++ b/dom/prio/PrioEncoder.cpp
@@ -100,23 +100,19 @@ PrioEncoder::Encode(GlobalObject& aGloba
       aRv.Throw(NS_ERROR_UNEXPECTED);
       return;
     }
 
     sSingleton = new PrioEncoder();
     ClearOnShutdown(&sSingleton);
   }
 
-  bool dataItems[] = {
-    aPrioParams.mBrowserIsUserDefault,
-    aPrioParams.mNewTabPageEnabled,
-    aPrioParams.mPdfViewerUsed,
-  };
+  nsTArray<bool> dataItems = aPrioParams.mBooleans;
 
-  PrioConfig prioConfig = PrioConfig_new(mozilla::ArrayLength(dataItems),
+  PrioConfig prioConfig = PrioConfig_new(dataItems.Length(),
                                          sPublicKeyA,
                                          sPublicKeyB,
                                          reinterpret_cast<const unsigned char*>(aBatchID.BeginReading()),
                                          aBatchID.Length());
 
   if (!prioConfig) {
     aRv.Throw(NS_ERROR_FAILURE);
     return;
@@ -127,17 +123,17 @@ PrioEncoder::Encode(GlobalObject& aGloba
   });
 
   unsigned char* forServerA = nullptr;
   unsigned int lenA = 0;
   unsigned char* forServerB = nullptr;
   unsigned int lenB = 0;
 
   prio_rv = PrioClient_encode(prioConfig,
-                              dataItems,
+                              dataItems.Elements(),
                               &forServerA,
                               &lenA,
                               &forServerB,
                               &lenB);
 
   nsTArray<uint8_t> arrayForServerA;
   nsTArray<uint8_t> arrayForServerB;
 

--- a/dom/prio/test/gtest/TestPrioEncoder.cpp
+++ b/dom/prio/test/gtest/TestPrioEncoder.cpp
@@ -23,20 +23,16 @@ TEST(PrioEncoder, BadPublicKeys)
   mozilla::Preferences::SetCString("prio.publicKeyB",
     nsCString(NS_LITERAL_CSTRING("badB")));
 
   mozilla::dom::GlobalObject global(cx, xpc::PrivilegedJunkScope());
 
   nsCString batchID = NS_LITERAL_CSTRING("abc123");
 
   mozilla::dom::PrioParams prioParams;
-  prioParams.mBrowserIsUserDefault = true;
-  prioParams.mNewTabPageEnabled = true;
-  prioParams.mPdfViewerUsed = false;
-
   mozilla::dom::RootedDictionary<mozilla::dom::PrioEncodedData> prioEncodedData(cx);
   mozilla::ErrorResult rv;
 
   mozilla::dom::PrioEncoder::Encode(global, batchID, prioParams, prioEncodedData, rv);
   ASSERT_TRUE(rv.Failed());
 
   // Call again to ensure that the singleton state is consistent.
   mozilla::dom::PrioEncoder::Encode(global, batchID, prioParams, prioEncodedData, rv);
@@ -167,19 +163,21 @@ TEST(PrioEncoder, VerifyFull)
     nsCString(reinterpret_cast<const char*>(pkHexB)));
 
   mozilla::dom::GlobalObject global(cx, xpc::PrivilegedJunkScope());
 
   nsCString batchID;
   batchID = (char*)(batchIDStr);
 
   mozilla::dom::PrioParams prioParams;
-  prioParams.mBrowserIsUserDefault = dataItems[0];
-  prioParams.mNewTabPageEnabled = dataItems[1];
-  prioParams.mPdfViewerUsed = dataItems[2];
+  FallibleTArray<bool> sequence;
+  *(sequence.AppendElement(mozilla::fallible)) = dataItems[0];
+  *(sequence.AppendElement(mozilla::fallible)) = dataItems[1];
+  *(sequence.AppendElement(mozilla::fallible)) = dataItems[2];
+  prioParams.mBooleans.Assign(sequence);
 
   mozilla::dom::RootedDictionary<mozilla::dom::PrioEncodedData> prioEncodedData(cx);
   mozilla::ErrorResult rv;
 
   mozilla::dom::PrioEncoder::Encode(global, batchID, prioParams, prioEncodedData, rv);
   ASSERT_FALSE(rv.Failed());
 
   prioEncodedData.mA.Value().ComputeLengthAndData();