Ok so i found the file. "/usr/share/applications/defaults.list" so for the gif image to open in web browser to need to add a line in web browser one and delete gif association with image viewer. root vi /usr/share/applications/defaults.list OR mentioned elsewhere that instead of always playing with root files; a user file would be a safer option... A defaults.list file with even one line that you require located in /home/user/.local/share/applications/ should override that one line in /usr/share/applications/defaults.list.
ladoga, mentioned elsewhere that instead of always playing with root files; a user file would be a safer option... A defaults.list file with even one line that you require located in /home/user/.local/share/applications/ should override that one line in /usr/share/applications/defaults.list. /