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Firefox completely fills up system drive with "invisible" data when left open.

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I have had this issue happen three times in the last several weeks: I suddenly get a notice from Windows that my system drive is full. I check the drive's properties in file explorer and it confirms zero free space. I run Treesize Free as admin, it reports that the drive is mostly empty. WinDirState reports the same. I close Firefox and the drive returns to its normal amount of free space after a minute (as reported in Windows drive properties).

This has happened on two separate Windows 10 computers (home, once, and work, twice), but I do have bookmarks, options, and add-ons synchronized on Firefox between these two computers, so it could be an option or an add-on causing the issue. The home PC's drive had approximately 20 GB free out of 120 GB and was the first one to run into this. While Firefox was running, I expanded the partition a couple of times, but the extra space filled up in minutes. The work PC's drive has 362 GB free out of 471 GB.

I don't have any way to reproduce the issue. It just happens occasionally over the last few weeks. I usually leave Firefox running all the time, and may have up to 20 or 30 tabs open.

Has anyone else experienced anything even remotely similar to this, or have any clues about what could be causing it?

All Replies (4)

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It sounds similar to this report, which we did not solve (yet?):

https://support.mozilla.org/questions/1327683

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If you open the about:profiles page you will find buttons to open your currently live profile folders (root directory, has the valuable data; local directory has cache and temporary stuff). You might want to check space on those two folders "before and after" to see whether either of them is experiencing extreme growth.

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Oh, wow, yes, that sounds like pretty much the same issue. Thanks! I had searched a few times before posting this and didn't find any previous reports. I guess I just didn't use the right keywords. I'll keep track at that thread.

Edit: found another thread, linked from the one you mentioned, about the same issue: https://support.mozilla.org/en-US/questions/1323378

Modified by mozilla.org13

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Thanks, looked at about:profiles. I will check the windows properties of those folders next time. i don't have much hope though, since the disk/folder/file size utilities (Treesize Free and WinDirStat) both missed whatever was causing the drive to fill up. But it doens't hurt to check next time this happens. I'll report back.

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