Whenever you save an html endless files get written to your HD. A way to avoid this is the format MHT developed by Microsoft for archiving. Their browser provides this in the standard version. It packs all those endless single files into one - and saves a lot of disk space.
Since this is a Microsoft idea Firefox does not support this - no idea why...
Without UnMHT I would NEVER use Firefox since I save many html files. UnMHT is great and even much, much better than the standard of Microsoft. For me it is the best Firefox Add-on of all.
There is only one problem - five stars for the rating are not enough for it!!!