Mostly useful for people who use Chrome, but most of these undoubtedly have analogues or versions in Firefox. A lot of good extensions for news, productivity and research, plus some stuff that's just plain cool.
While this website is helpful, many of the apps do not seem to be useful to everyday browsing, excluding a few in the Education section of the article. Granted, I still went and downloaded a lot of those apps because, as Nathan said above me, they're pretty cool.
Browser extensions are definitely neat -- all the browsers have them now, pretty much. Firefox was the first browser to be extensible like this, so there tend to be a lot of extensions available for it. Zotero, which we're going to learn about next week, started out as a Firefox extension.
I thought about defining "extension" in core concepts, but it's maybe a little more advanced than that. Extensions (also called "add-ons" and "plugins") are basically little apps that "plug in" to a big app.