There are several Facebook applications that let you import your Flickr photostream to Facebook, but photos appear in a separate box on your Profile. None of these apps lets you upload photos directly to Facebook photo album, so you could tag them in a way Facebook understands, mark your friend on them etc.
This method uses the unofficial Flickr2Facebook uploader by Keebler. To use it you will need:
-Greasemonkey addon for Facebook
Step 1: Install Gresemonkey for Firefox
Firefox Add-ons page and Install Greasemonkey
This is a very powerful Firefox add-on and it will come in handy for many things, not just uploading photos to Facebook, so it is worth to have it installed.
If you already have it you can skip this step.
You need to do this step only once.