Rated 5 out of 5 stars
This thing simply rocks! Slowly replacing Evernote with this but I am still working out all the options and kinks due to other extensions.
For example Download Statusbar will not allow me to open Diigo's Bookmark window in order to edit my tags. No contest, Diigo wins! Bye bye, Download Statusbar.
I also have trouble keeping it signed in between browsing sessions (only full FF shutdowns, not quick restarts.) I have so many security add-ons though that I haven't determined which is at fault. However, most of the time it works to enable third party cookies temporarily. (In FF options>privacy>tick third party cookies, login to Diigo, then disable the third party cookies again.)
Strangely, Diigo seems to do better when I don't Whitelist it in all of my security extensions. I haven't determined which ones cause the annoyance though. I will post back when I find out. What I have installed is Noscript, Refresh Blocker, Flashblock, Better Privacy, and Redirect Remover. (I'm not paranoid. Really! I'm just hiding from a big, secret conspiracy. Sshhhh!) :-D