The question you need to ask yourself is this:
How would we fix the issue if the file exists and can be downloaded (Something you can check using the principles outlined in that log entry), but clicking on the button to download it doesn't work?
The answer is that you can't, you are testing browser functionality. You cannot fix a browser bug and release a new version of the browser. Even if you could, you can't force your user to use the new updated version of the browser.
By all means check that the file is there and can be downloaded, however don't waste your time trying to test browser functionality that you have no control over.