Hi bbp,
Thanks for the clarification. I have dealt with a few customers who were also unable to see the "Custom Item Specifics" link and, in each of those cases, we ended up determining that the Ad Block Plus add on for Firefox was blocking the link from loading on the listing creation page so perhaps the same is true about your situation.
If you are using the Ad Block Plus add on for Firefox, you should see a red stop sign icon that says "ABP" within it in the upper right corner of your browser. If you click the arrow next to that icon while on the Auctiva site, you should see the option to disable it for Auctiva.com or disable it altogether.
If you are indeed using Ad Block Plus, I expect that you will be able to see the Custom Item Specifics link once you have disabled it, at least for the Auctiva.com site.
If you need further assistance with this issue after exploring this possibility, please contact our customer support team by mousing over the "Help" tab within your account and selecting the "File Support Case" option and we will be happy to continue working with you on this.
-Mike