Of the ones on your list, my faves are DownThemAll, TabMixPlus and de.icio.us. I use IE View Lite rather than IE View, but it is a lifesaver at work where I have no choice but to use IE for many of our intranet sites. I didn't like Google Browser Sync, and just uninstalled it recently. There are a whole bunch which are just always there, and seem less like an extension, but a seamless part of the browsing experience, McAfee Site Advisor, FoxClocks, Auto Copy, Stylish. Plus the 2 email notifiers, Gmail Notifier and Yahoo Mail Notifier. Firebug and Web Developer are great when I'm putting together a new web page. Finally, ProxyButton. I have to use a proxy at work, don't at home, swapping with just a single button click is a so much more convenient.
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