Maybe old news for most, but I found this recently and it's pretty nice -- one can preview in two "mini" browser sizes. I find it a time saver and nice for image and visual content sites.
Here's the description from the developer
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i tried this ~ a year ago. i found it annoying as when you leave your mouse pointer alone over ANYTHING that is a link a window pops up. So I had lots of unwanted popups.
I think I know the one you are talking about -- can't remember the name offhand. What that one does is what you say, i.e. you hover over a hit in Google, and pop. I got rid of that one, drove me nuts too.
This one is only activated when one hovers over over a the actual tab above the browser window in Firefox as far as my experience.
No good on links in a page (pun unintended, but that's good :).