Download Firefox add-ons link: Interclue :: Add-ons for Firefox
I searched and saw that Interclue had been mentioned in various parts of DCF (including this thread, I think), but thought I should mention it again.
I installed Interclue after reading the comments on the Add-ons page which seem to suggest that it is "broken". However it has an up-to-date signature and, after installing it, I was pleasantly surprised to find that it seems to work fine so far, though I haven't tested all of its functionality.
I seem to recall using something similar some time back that gave a "look-ahead" for any link and I dumped it because it was invasive and didn't give the user much control over what was to be viewed.
However Interclue has a really detailed set of options and is fully controllable and not
invasive, furthermore, it does a lot more than just "look-ahead".
Well worth a look-see IMHO. Could be a potential RAM, CPU and bandwidth resource hog though - but these behaviours too can be constrained via the options.