The popups cannot be re-triggered directly, however all popup events (earnings, image acceptance, blog posts, image requests etc) add an entry to the picNiche notifications panel in the picNiche sidebar.
To open this, left-click on the P-icon in the status bar of your browser (you might need to enable the 'addons bar' depending on your firefox version) OR goto Tools/picNicheTools/Sidebar. The notifications sub-panel should be expanded by default, but if for reason it is not, just click where it says Notifications and all the popup entries for the current browser session (ie. since the last browser restart) will be in there.
Bob