September 30, 2019
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You’re using Firefox with the uMatrix add-on to fine-tune what can and cannot be done by a remote website on your browser.
But when you right-click something and choose “Save Link As” or some variation you get the following error:
Download Cannot Be Completed Message from uMatrix
The download cannot be saved because an unknown error occurred.
Please try again
So what you need to do is open the uMatrix log, and look for the line in red showing that a request has been blocked. It will look something like this:
Then open the uMatrix settings and visit the “My rules” tab, then add a line to the “Temporary rules” with those highlighted fields:
twdown.net video.twimg.com other allow
Then click Save, followed by <- Commit.