Rated 3 out of 5 stars

this add-on, for some reason, isn't maintained anymore.. at least on Linux platforms.

i use the renewed Thumbnail Zoom Plus (look here: https://addons.mozilla.org/en-US/firefox/addon/thumbnail-zoom-plus/ )

since the Plus one isn't yet reviewed by Firefox/Mozilla (as of Nov. 2011) you're using quite a beta version of the add-on.. it's close to perfect, but there are issues.. like overlapping the cursor and so forth..

enjoy :)