Dear nikolay.parfianovich, The step you are describing with the image cannot be deactivated. In firefox you must click on open file with ... The second point in the image.

I hope I have been helpful

Note that you should never select "Firefox Web Browser" (second choice in the screenshot) as the application to handle a file as this is a dangerous choice that can lead to tabs being open endlessly.

• https://support.mozilla.org/en-US/kb/firefox-repeatedly-opens-empty-tabs-or-windows

You get the choice to open the file in Firefox (first choice: Open in Firefox) when the server sends the file as a generic content type like "application/octet-stream" or as "content-disposition:attachment". In that case Firefox offers to open the file in a tab. The file is still downloaded and saved to the temp folder as you can see by the file:// link in the location bar.

You can't save this choice as an automatic action and you will always have to confirm this.