Source: https://github.com/MrAlex94/Waterfox/commit/45130a237874aaa96bdf23ee107b0be0e0a2afab?diff=unified#diff-9517c6ca41ff7c9627f13ff83c2f7dce
Date: 2020-01-30 09:22:35 -0500
diff -x '*.swp' -x '*.orig' -x '*.diff' -x '*debhelper*' -Naur 1/js/xpconnect/src/XPCVariant.cpp 2/js/xpconnect/src/XPCVariant.cpp
--- 1/js/xpconnect/src/XPCVariant.cpp	2020-01-09 15:53:52.000000000 -0500
+++ 2/js/xpconnect/src/XPCVariant.cpp 2020-01-30 09:14:14.645389196 -0500
@@ -180,7 +180,7 @@
             type = tDbl;
         } else if (val.isBoolean()) {
             type = tBool;
-        } else if (val.isUndefined() || val.isSymbol() || val.isBigInt()) {
+        } else if (val.isUndefined() || val.isSymbol()) {
             state = tVar;
             break;
         } else if (val.isNull()) {
@@ -275,8 +275,8 @@
         mData.SetFromBool(val.toBoolean());
         return true;
     }
-    // We can't represent symbol or BigInt on C++ side, so pretend it is void.
-    if (val.isUndefined() || val.isSymbol() || val.isBigInt()) {
+    // We can't represent symbol on C++ side, so pretend it is void.
+    if (val.isUndefined() || val.isSymbol()) {
         mData.SetToVoid();
         return true;
     }