Web browsers and "site data" stored locally

I've tried googling a bit and haven't find useful information on what "site data" actually is. For example, Firefox tells me that cartridgesave.co.uk has 44.8MB of site data on my computer and even if that was how much is in the browser cache for that site, it would make more sense but it's still a bit high. I go on that site from time to time (maybe once every 2-3 months), Firefox tells me that the last time I visited that site was 3 weeks ago. It still seems... excessive. I know I can clear that bit of data and I do go through on a per-site basis clearing out random sites I've looked at, but I'm not sure that site data is actually the browser cache as Firefox offers for me to clear out various elements for all time, and "cookies and site data" is one option, then the next option is "temporarily cached files and pages". Admittedly the two figures it offers me total up to the total figure that Firefox reckons my site data is (the figure directly above 'manage site data' in... Read more