Why:
Currently when you download a file the browser will prompt you where to save it and will proceed as such. However, if the file doesn't exist on the server and the server returns an HTTP 404 error, the browser won't tell you and will just download that error page and save it as the file you wanted.
Only afterwards when you try to open the file will you realize it is not what you wanted.
How:
This add-on will perform 2 checks to make sure the file is the one you wanted.
Firstly, if the downloaded file is less than 4 KB it will show a notification telling you so. A file less than 4 KB should rarely happen.
Secondly, if the file download request was responded to with a 4XX or a 5XX error, it will also show a notification telling you so.
Clicking on the toast notification will open the folder containing the downloaded file.
Permissions Disclosure:
This add-on needs the following permissions:
Access your data for all websites: Needed to identify when HTTP 4XX/5XX errors occur and see if they occurred while downloading a file. This should not affect performance because only web requests belonging to the "miscellaneous" category get sent to this extension.
Read the browser's download history: Needed to identify the size of files after they have downloaded
Display notifications to you: Needed to show information to you using the browser's notification panel
