Mostly useable. Such potential! Rated 4 out of 5 stars

So far, I have been very pleased with Diigo and believe it has great potential. Having used it for some time, I do however notice a few things which stand between it being a good program and a professional, intuitive tool.

- Lists:
Bookmarking works fine, as does tagging. You can also categorise your bookmarks into 'Lists' (e.g. I would put items tagged 'dogs', 'cats', and 'fish' all under the list 'Pets'). However, it is extremely frustrating that these Lists do not prevent the creation of multiple copies of the same item. When a bookmark is (accidentally) added to the same List on two separate occasions, that List's item count goes up (eg. "Showing 20 of 20" becomes "Showing 20 of 21"), and the bookmark is displayed multiple times under the "By Time" tab. There is no intelligible reason as to why Lists should function this way. In fact, for people such as myself who use lists as a sort of "ordered checklist of sites to visit", it wastes my time by sending me to the same page repeatedly. Also, it causes the item count on my lists to grow incredibly daunting - even when I actually end up having few items. This makes me misjudge the amount of time needed to visit all the bookmarks on my List, and affects my overall time-management! Such duplication within Lists needs to be written out of the program so that Diigo can be put to professional use.

- Simultaneously adding a tag to multiple bookmarks:
If I want to add a specific tag(s) to two or more bookmarks, I have to either edit each bookmark separately, or check all the relevant ones, choose 'Edit' in the drop-down menu at the top of the page, and then manually type each tag for each bookmark into the textbox that appears. An example of a more desirable method can be found on Gmail, where I can "label" several messages simultaneously by checking all the relevant messages and choosing the desired label from a drop-down menu. Using the same method - just substituting messages for bookmarks and Labels for Tags - Diigo could instantly become a far more usable tool. My lengthy observation of the Diigo Forums shows that I am not the only user looking forward to this innovation. The user drojack has posted the same suggestion (

- Different versions of the same tag:
When I search through my bookmarks by tags, I sometimes do not get all the results I want because some of the relevant bookmarks have accidentally been tagged under a slightly different version ( e.g. some relevant bookmarks are tagged "community", others are tagged "communities", others are tagged "comunity", etc.) It is difficult to remember the exact conjugations of words that already exist in your tagcloud, especially when you use Diigo a lot and have a great variety of tags. Furthermore, one can easily misspell a word and thereby accidentally create a new tag. To prevent this, I suggest that the Diigo form for creating new bookmarks should anticipate which tag the user is entering when creating a new bookmark. A wonderful example of this was the drop-down menu which used to be available on the form, but which is unfortunately no longer there (at least in my Firefox browser). An alternative and even better system would the one used by the Firefox extension "Bookmark Tags". Let's say I want to create a new bookmark using Bookmark Tags, and I want to tag it 'french'. When I bookmark it and type 'f' into the 'Tags' text box, it alphabetically suggests the first tag that I already use beginning with 'f' (e.g. 'facebook'). When I continue typing, it automatically changes its suggestion, whilst still suggesting existing tags ( e.g. 'facebook', - 'free' - 'free' - 'french '). If 'french' is a tag I have not used before, it will stop making suggestions after I have typed 'frenc'. I then simply finish typing the word, and Bookmark Tags recognises it as a new tag. Using this kind of system, Diigo users can more efficiently create and retrieve both bookmarks and tags.

- Lack of means to contact the developers:
Last but not least, I am rather disconcerted by the fact that the users' only means of (perchance!) reaching the developers is through the Community Forum. I searched the entire site and was not able to find a single e-mail address for "User Support", "Helpline" or anything to that effect (instead, I found this info-email for people interested in "partnerships, investment, licensing, and career opportunities"). A more direct line of communication would benefit not only the users and the community, but also the developers and the program.

That being said, Diigo is generally a functional and time-saving utility. It bookmarks correctly, the tagcloud is efficient, highlighting is a dream come true, and its stickies are downright practical. Most of the problems mentioned here do not impede the day-to-day use of the program; their improvement would simply provide an even more gratifying user-experience.
I still recommend - just be aware the issues above :) (and perhaps take a look at the review by Peter below)

This review is for a previous version of the add-on (0.5.2007021000). 

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TrulyFrancesca and Peter,

Most of your problems have been addressed. Also, the toolbar here on Mozilla is often not as up to date as the one on our website.