Allow to specify only the path instead for export to file system

[SebastianZ]

The preference extensions.firebug.consoleexport.logFilePath added in 22bddbd allows to specify a file, to which the data is exported automatically.

Though as mentioned in Google Code issue 5182 comment 22 it would be nice if you could just specify the path and the file name would be automatically generated using the page's domain name like NetExport does it.

This allows to save your output separately for each page you visit.

The implementation could offer both functionalities. I.e. if a full file path is specified, the data is saved to that file, always overwriting it. If a directory path is specified, the file name is dynamically generated using the domain name.

Sebastian