Here is a list of tips and advice on using Firefox for scraping, along with a list of useful Firefox add-ons to ease the scraping process.
Therefore, you should keep in mind the following things when working with Firefox and XPath:
Firebug is a widely known tool among web developers and it’s also very useful for scraping. In particular, its Inspect Element feature comes very handy when you need to construct the XPaths for extracting data because it allows you to view the HTML code of each page element while moving your mouse over it.
See Using Firebug for scraping for a detailed guide on how to use Firebug with Scrapy.