The onlinehelp viewer can be selected.
If it shall be done via netscape remote-commands,
you have to enter the keyword "netscape-remote" as viewer.
Netscape must be running.

The helpfiles are located in PATH_SANE_DATA_DIR/
(this is typlically /usr/local/share/sane).
The file that is loaded is sane-backendname-doc.html,
the backend may use more html-files:
sane-backendname-*-doc.html

Images that are only for the backend helpfile should
have the name sane-backendname-*.*