In the previous spec for IndexedDB (http://www.w3.org/TR/2011/WD-IndexedDB-20111206) the mode value for IDBDatabase transaction was a short. In the current spec (24 May 2012) it is now a string. FF12 still uses a short. The mode value determines whether you want a read-only transaction or a read-write transaction.
Does anyone know where to find out the progress of IndexedDB (ie when will it be done and we can use window.indexedDB instead of window.mozIndexedDB/webkitIndexedDB/msIndexedDB)? Unfortunately the spec gives no indication if this is a proposed "final" version or just one of many to come (with more breaking changes).