I know from Googling what it does and what its purpose is. However, for something that’s supposed to be updated daily, it hasn’t been updated since late 2008. Does that mean that I can delete it? Or does FF12 still use the file?
If you delete it, Firefox will just create another one, assuming the file is still being used. Mine apparently is using urlclassifier3.sqlite.
Note that the new version will be a lot smaller, although it will contain the same data. Apparently Firefox doesn’t ever vacuum this database, which means that, every time the file changes, it just gets bigger.