Show the issue. What linux and window OS are involved? What desktop? X11 or Wayland? Show that your OS is seeing the mounted drive. I'll try and replicate using openSUSE and Win7 / win11 dual boot I have.

Here is a screenshot showing Firefox saving to a usb I plugged in. see screenshot You can clearly see that my file manager (Dolphin in KDE) is showing the drive and Firefox file picker can also see the drive.

Thanks for your kind help!

Ubuntu 25.10 with default GNOME desktop, on Wayland.

$ df -h Filesystem Size Used Avail Use% Mounted on tmpfs 6.1G 2.4M 6.1G 1% /run /dev/nvme0n1p4 98G 60G 34G 64% / tmpfs 16G 72M 16G 1% /dev/shm efivarfs 268K 235K 29K 90% /sys/firmware/efi/efivars tmpfs 5.0M 8.0K 5.0M 1% /run/lock tmpfs 1.0M 0 1.0M 0% /run/credentials/systemd-journald.service tmpfs 1.0M 0 1.0M 0% /run/credentials/systemd-resolved.service tmpfs 16G 37M 16G 1% /tmp /dev/nvme0n1p1 256M 49M 208M 19% /boot/efi /dev/nvme0n1p3 200G 119G 82G 60% /mnt/Windows /dev/nvme0n1p5 652G 198G 455G 31% /mnt/Data tmpfs 3.1G 144K 3.1G 1% /run/user/1000

$ cat /etc/fstab /dev/disk/by-uuid/ea9a9e84-b469-43fd-969f-b64728417baa / ext4 defaults 0 1 /dev/disk/by-uuid/ECA5-E4C3 /boot/efi vfat defaults 0 1 /swap.img none swap sw 0 0 /dev/disk/by-uuid/222CDAF12CDABF4B /mnt/Data auto nosuid,nodev,nofail,x-gvfs-show,uid=0,gid=6,umask=007 0 0 /dev/disk/by-uuid/F47CA6A97CA665D8 /mnt/Windows auto nosuid,nodev,nofail,x-gvfs-show,uid=0,gid=6,umask=027 0 0

Picture 1: I tried to save this page to the disk. The mounted path can be found in the popup window and I clicked the Save button. Pictures 2 and 3: I opened the file browser to check the saving results. There are empty webpage HTML and resource files created. And the reported error message is present in Firefox.

Can you do it in any browser? Can you just place any file on the c drive via drag and drop?

Tried on my dual boot with Win11 and even root cannot access windows c drive. see screenshot This will need to further research, but Win11 will be going away soon. I do have another dual boot with win7 and I do recall being able to access the c drive after just putting in the root password. Let me see what happens on that laptop.

I think it's just a permissions issue. It works for me on win7. I'll need to go back to win11 dual boot and check permissions because the error I get on win11 is about permissions. see screenshot in previous post Need to run mount to see the permissions of the filesystem. see my screenshot

/dev/sdb2 on /run/media/jonzn4suse/2FEF88FCD46B8F12 type fuseblk (rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other,blksize=4096,uhelper=udisks2)

Thanks a lot for the above!

On my PC, it works well for Chrome to save things to the mounted places. I can create files to the mounted place with the file browser or from the shell.

$ mount | grep Data /dev/nvme0n1p5 on /mnt/Data type fuseblk (rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other,blksize=4096,x-gvfs-show)

I also think it's just a permission problem. But clearly it's not the write permission that has been denied, as the empty files can be created. The file system is NTFS and syscalls like chmod can return EPERM.

The things are more complicated than I thought.

I just tried creating a directory with the user running Firefox as the owner and with mode 777. Then I tried saving files with Firefox into the directory to find it also failed. It seems that NTFS is not special here but there could be something wrong with the permission passing to the process saving files to disk for Firefox. (I can save things with Firefox normally to the home directory and any subdirectories.)

It's also strange that this never happened at the time when I used Ubuntu 24.04, for more than one year, while keeping the Firefox up-to-date through deb packages provided by mozillateam's ppa.