The plugin uses the Metafizzy Isotope extension to create a grid system that displays the thumbnails. The number of columns or rows can either be determined automatically or controlled via settings that you can find in the “Pagination Settings” Tab.
However, the Metafizzy Isotope extension is a very popular extension and many other plugins use it as well, along with many themes, potentially causing WordPress to load the file multiple times, which can create problems. One indicator that the file has been loaded by multiple plugins and or the theme as well, is that the thumbnails are not displayed in a grid system but are all aligned to the left instead (with one thumbnail per row).
The “jQuery Facebook Gallery WP” plugin allows you to disable the loading of the Metafizzy Isotope extension in the Tab called “Extension Files”. Once you uncheck the checkbox “Load Isotope File” and save the settings, the plugin will not load that file and instead rely on other plugins or the theme to load the file instead. Usually, that will fix the problem. If the Metafizzy Isotope extension file is still loaded multiple times, you need to check all the other plugins or the theme of your website to see if they provide a similar feature.
Please ensure that the Metafizzy Isotope extension file is loaded only one!