Yes, you should be able to safely do this. This is a really large folder to have in Firefox and most likely 1 or 2 sites have decided to save that much data in Firefox. Use this thread & the article below as a guide: What is in the profiles/storage/default folder? https://support.mozilla.org/questions/1349530 https://support.mozilla.org/en-US/kb/storage#w_delete-site-storage-for-individual-websites You should be able to see which websites have the largest sizes when you get to the "Manage Data" area of Firefox. It's located on the Settings page, Privacy & Security panel. It's in the Cookies and Site Data section. You will see a "Manage Data" button there. Let us know what you find. Remember that clearing data like this sometimes logs you of the website or removes saved text you may have filled out somewhere on the site. I don't think any important data is saved here but for some reason some sites grow these folders to insanely large sizes & do not clear the data on their own. It could be something like a very large amount of cookies.