This is a brief overview of things you can do with fireflix.
First, you should proceed with authorization. If you haven't done it yet, it should happen automatically once you open fireflix sidebar. To clear authorization token off of the preferences, right-click on the 'Authorization info' part of the sidebar and select 'Sign off' from the pop up menu.
Basically, you can search flickr photos here. Either all or yours (keep 'mine' checked to search your own photos).
Once you have acquired search results you can browse through them. To open any particular picture in a new tab either doubleclick it or hit ENTER.
While moving through the list of pictures found you should have a little preview at the bottom of the window.
This is where you can browse your sets. You can edit some sets properties here and, most importantly, you can generate HTML of linked thumbnails for sets contents. Use your right mouse button on the photoset.
To upload pictures you don't even have to select this tab. Drag'n'drop into fireflix sidebar should do. There is nothing wrong with going into the tab and using 'Add' button either.
You can add photos to the list, edit their titles and/or tags and once you're done with it, trigger upload procedure. Once your images have been uploaded, you will be prompted to create a photoset for newly uploaded photos. You don't have to, though.
As the extension is at the very early stage of development, feel free to provide feedback at http://kin.klever.net/fireflix/feedback/.