It is FasterFox: http://fasterfox.mozdev.org/
It makes your Firefox faster.One of the great functions is "Prefetching."
After you install the add-on, fasterfox will pre-load every possible links while you read the web page.
The meaning of the word, "Prefetching," is ambiguous.
FasterFox explains the meaning in its setting dialog:
Utilizes idle bandwidth to silently download and cache links in the background so they may be ready for immediate display by the time you click them.Actually it is dangerous in some cases, because the prefetching presses every links in order to get the next pages. Some of links might be "delete something" or "purchase something." Therefore fasterfox has limited policy for the prefetching.
You can find more information here:
This add-on increased not only quantitative speed, but also qualitative feeling. I strongly recommend you.