mixmax, I coded some bash scripts to make easier to use delicious; http://github.com/azer/bookmarking-tools. Using dmenu (suckless.org) with these scripts, it's very comfortable to access bookmarks on desktop. I don't know the Firefox 4 way of executing a bash command but UZBL users can also bind a key like "b" to insert new bookmark to both a local file and to delicious.