diff --git a/CHANGELOG.md b/CHANGELOG.md
index de32b668d7..aee736f54d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - fixed compatybility issue with MSEdge 112.x
 - fixed updter issue [#2790](https://github.com/sandboxie-plus/Sandboxie/issues/2790)
 - fixed new box wizard issue [#2792](https://github.com/sandboxie-plus/Sandboxie/issues/2792)
+- fixed issue with firefox/thunderbird [#2799](https://github.com/sandboxie-plus/Sandboxie/issues/2799)
 
 
 
diff --git a/Sandboxie/core/drv/ipc.c b/Sandboxie/core/drv/ipc.c
index 3149d9cd20..642da0f66b 100644
--- a/Sandboxie/core/drv/ipc.c
+++ b/Sandboxie/core/drv/ipc.c
@@ -1444,12 +1444,30 @@ _FX NTSTATUS Ipc_Api_DuplicateObject(PROCESS *proc, ULONG64 *parms)
 
     if (NT_SUCCESS(status)) {
 
-        status = NtDuplicateObject(
-            SourceProcessHandle, SourceHandle,
-            TargetProcessHandle, &DuplicatedHandle,
-            DesiredAccess, HandleAttributes, Options);
+        HANDLE SourceProcessKernelHandle = (HANDLE)-1;
+        HANDLE TargetProcessKernelHandle = (HANDLE)-1;
 
-        *TargetHandle = DuplicatedHandle;
+        if (!IS_ARG_CURRENT_PROCESS(SourceProcessHandle)) 
+            status = Thread_GetKernelHandleForUserHandle(&SourceProcessKernelHandle, SourceProcessHandle);
+        if (NT_SUCCESS(status)) {
+
+            if (!IS_ARG_CURRENT_PROCESS(TargetProcessHandle))
+                status = Thread_GetKernelHandleForUserHandle(&TargetProcessKernelHandle, TargetProcessHandle);
+            if (NT_SUCCESS(status)) {
+
+                status = ZwDuplicateObject(
+                    SourceProcessKernelHandle, SourceHandle,
+                    TargetProcessKernelHandle, &DuplicatedHandle,
+                    DesiredAccess, HandleAttributes, Options);
+
+                *TargetHandle = DuplicatedHandle;
+            }
+        }
+
+        if (SourceProcessKernelHandle && !IS_ARG_CURRENT_PROCESS(SourceProcessKernelHandle))
+            ZwClose(SourceProcessKernelHandle);
+        if (TargetProcessKernelHandle && !IS_ARG_CURRENT_PROCESS(TargetProcessKernelHandle))
+            ZwClose(TargetProcessKernelHandle);
     }
 
     //