hwnd := WinExist("ahk_class MozillaWindowClass")
GetClassLong := DllCall("GetClassLong" (A_PtrSize=8 ? "Ptr":""), "Ptr", hwnd, "int", -26)
if A_LastError != 0
   msgbox % "GetClassLong error:`n" GetErrorString(A_LastError)
DllCall("SetClassLong" (A_PtrSize=8 ? "Ptr":""), "Ptr", hwnd, "int", -26, "Ptr", GetClassLong | 0x20000)
if A_LastError != 0
   msgbox % "SetClassLong error:`n" GetErrorString(A_LastError)
return



GetErrorString(Errornumber)
{
	VarSetCapacity(ErrorString, 1024)		;String to hold the error-message.
	
	DllCall("FormatMessage"
			, UINT, 0x00001000			;FORMAT_MESSAGE_FROM_SYSTEM: The function should search the system message-table resource(s) for the requested message.
			, UINT, NULL					;A handle to the module that contains the message table to search.
			, UINT, Errornumber
			, UINT, 0							;Language-ID is automatically retreived
			, Str, ErrorString
			, UINT, 1024					;Buffer-Length
			, str, "")					;An array of values that are used as insert values in the formatted message. (not used)
	
	StringReplace, ErrorString, ErrorString, `r`n, %A_Space%, All		;Replaces newlines by A_Space for inline-output
	
	return %ErrorString%
}