If you visit images/
algar.jpg is not there - so the file isn't uploaded.
Also I've found that if you have...
$WAGLOBAL_Images_Folder = "../images/";
..in your globals file then the page code will read.. "http://studio-n.se/CMS100/../images/algar.jpg"
i.e. the ../ is inserted. Internet explorer corrects/removes the ../ from the code and dislays the image but Firefox doesn't and displays the 'x' instead.
Cganging the globals line to...$WAGLOBAL_Images_Folder = "images/";
...seems to resolve this issue.
Hope that helps,