The reason for the odd behavior of Chrome seems to be a if/else construct that is repeated throughout the source of runtime.cc:


// Check if the name is trivially convertible to an index and get
// the element if so.
if (name->AsArrayIndex(&index)) {
return GetElementOrCharAt(object, index);
} else {
PropertyAttributes attr;
return object->GetProperty(*name, &attr);
}


Chrome makes a difference between properties and elements. And they do weird type casts. If you check JavaScriptCore, you see there is a better way:

inline JSValue JSObject::get(ExecState* exec, const Identifier& propertyName) const
{
PropertySlot slot(this);
if (const_cast(this)->getPropertySlot(exec, propertyName, slot))
return slot.getValue(exec, propertyName);
return jsUndefined();
}


It can’t be, that a browser with 4 open tabs requires about 600 MB of memory. That’s 150 MB per Web site, which seems a bit too much

Safari, by the way, requires 128 MB for 5 open tabs.

If you find that Firefox’s memory usage continues to grow after long periods of being open, you may want to consider periodically restarting Firefox to bring the memory usage back to reasonable levels.

http://kb.mozillazine.org/Memory_Leak