I fixed this by adding the following to the thumbnail image style in nggallery.css:
.ngg-gallery-thumbnail img {
float: left;
...
}
(Also tested in ff, ie7, ie6.)
It will increase the horisontal thumbnail spacing in ie6, which can be slightly remedied by using padding instead of margin on the thumbnail container as follows (for those who care about ie6):
.ngg-gallery-thumbnail {
/*margin-right: 5px;*/
padding-right: 5px;
...
}
