Consider adding a Remove method on nsBaseHashtable::EntryPtr (added in bug 1371094). This is for cases where LookupForAdd is preferable over Get+Put for performance, but we have some exceptional cases (errors or reaching a max entry count, etc) where one needs to remove the speculatively added entry. One could also imagine having a auto-Remove feature such that if OrInsert is never called on a newly added entry, it is auto-Removed in the dtor. Example: auto entry = hashtable.LookupForAdd(key); if (entry) { // OK, it existed already } else { entry.AutoRemoveIfNotAssigned(); // complex code to initialize the new value here... if (NS_FAILED(rv)) { return; // the new entry is Remove'd by the dtor since we never reached OrInsert } entry.OrInsert([&value](){ return value; }); }