Also what is to be considered is that the ONLI site is Old Norse or Old Icelandic not Icelandic, so the two will differ. The Vigfusson dictionary  is out of print and it costed around $500. The  Zoega dictionary  is the second best Old Norse dictionary available (I also use that as a source) and I believe is also unable and that resource I am sure would cost over $200. So I am using the best resources available. This is just to clarify resources that are used on the ONLI site  and I don't deviate from them. 
 
I also have the E.V. Gordon intro to Old Norse but it really is not of much use. One, it has ON texts, those are available on-line.
Two, the dictionary at the back is sparse at best, like 30 pages worth, unlike Vigfusson which about 20 times larger or about 1000 pages with double columns and small fonts..
Three, I personally find the grammar section to of the most value. All the resorces that are available to everone, the easier it will be to learn Old Norse and thats why I post that ONLI has a site with ON linguistic tools that may aid people who are seeking to learn this largely inacessible language. 
 
 
Anthanarik
 
 
Anthanarik