Greetings to the Group.. I have had two cases in the last 48 hours where the usable disk space on my system went to zero bytes available. Both cases simply closing Firefox resolved the issue (within about 5 minutes). Details: System - Windows 10 1909 - Patched 12/14 with December updates Firefox version 84.0 (64 bit) - auto updated likely on 12/14. I am running a 2TB SSD with about 1.5TB free. On Thursday (12/16/2020) when I connected to the machine I had zero bytes available and FireFox was using 12G of physical memory. I only had 3-4 tabs open in two separate windows (mostly local admin web sites). On Friday (12/17/2020) I was down to around 400G available before closing and restarting Firefox. The system stays online most of the time and I usually have FireFox open with tabs in the background. I ran a disk usage using the SysInternals DU tool both when I had 1.5TB free and when I was down to about 400G free and did not see anything significantly different between the two reports. I had a colleague running an Intel MacOS and the most recent version of Firefox mention that his had seen a similar issue missing over 56G of disk space. I have no addons installed within FireFox at this time.