Works well Rated 4 out of 5 stars
GMarks works very well. I am looking for something that can behave identically to the bookmarks button on the (currently unsupported) Google Toolbar. GMarks doesn't do that (and at present, nobody else's Google Bookmarks add-in does either) but it works very well.
The only real problem I've had is that by default, it installs as a menu bar item, and menu bars are hidden by default in current versions of Firefox. It should auto-add something else (perhaps a toolbar icon) or do something else so new installations will realize that it did install OK. Also, when customizing toolbars, the icon for the GMarks folder seems to be absent, so it renders as some other icon, and doesn't have any text in the customize dialog.
But these are minor features. Overall, GMarks is a great add-on.