Suppose browser $A$ finishes loading a given page in five seconds, while browser $B$ completes in half the time.
How many times faster is $B$ than $A$? Well, twice, of course. But what about the inverse? How many "times faster" is $B$ than $A$?
One way to answer this is to assume that "$-x$ times faster than" just means "$1/x$ times the speed of". The intuitive problem with this is determining how much faster something is moving compared to something moving slower than it. It's just a really awkward way of putting it, but basically we can look at the number of "times faster" as a negative or a fractional value.
They're both more or less valid interpretations.
Now if we ask the question, how many times slower than $B$ is $A$, we get the original answer -- it's twice as slow.
So how many times faster is it? It depends on which interpretation we're using. It's correct to say that it is -2 times "as fast" since it is twice as slow; but also (and more intuitively) correct to say the speed of $A$ is 0.5 times the speed of $B$.