The right click menu on the floppy drive icon should have the 'Format'
option so try that and see if the disc is able to be formatted. Also
try another blank floppy just in case it's a bad one.

Just a point or two - why bother with floppy discs when the USB flash
drive is so much easier to work with ? Presumably you backup your data
somehow ( external HD perhaps ? ) and that's also a better place to
export your bookmarks to.