Doesn't support "file:///" tabs

[irvnriir]

If that doesn't require more Permissions, i think it should work for such tabs as for any other .

[Tim Weißenfels]

Unfortunately it is not possible: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/tabs/create

For security reasons, in Firefox, this may not be a privileged URL. So passing any of the following URLs will fail: [...]

• file: URLs (i.e., files on the filesystem. However, to use a file packaged inside the extension, see below)

Just in case I wrote a small test extension to verify this:
local_file_access_test-1.0.zip

I wish there was a special permission for this but right now there isn't. Let me know if I missed anything, otherwise please close this issue.