The one in Voetboogsteeg actually is the oldest address for "Vlaamse Frieten" in Amsterdam.
What is now the fashion , in stead of mayonaise is the Joppiesauce , a bit more spicey !
Check this "culinary" website with lots of Amsterdam pics, to start with the Vlaamse Frieten under Continental Hotel at Damrak :
http://www.renesmurf.nl/pivot/entry.php?id=1025
or this one:
http://www.belgianfries.com/
the original Belgian Fries website (in English) , you can see the "Frietkots" , the primitive selling points that were (here and there still are) typical for Belgium.