browse-url-filename-alist is a variable defined in `browse-url.el'.
Its value is

(("^/\\(ftp@\\|anonymous@\\)?\\([^:]+\\):/*" . "ftp://\\2/") ("^/\\([^:@]+@\\)?\\([^:]+\\):/*" . "ftp://\\1\\2/") ("^/+" . "file:///"))

An alist of (REGEXP . STRING) pairs used by `browse-url-of-file'.
Any substring of a filename matching one of the REGEXPs is replaced by
the corresponding STRING using `replace-match', not treating STRING
literally. All pairs are applied in the order given. The default
value converts ange-ftp/EFS-style file names into ftp URLs and prepends
`file:' to any file name beginning with `/'.

For example, adding to the default a specific translation of an ange-ftp
address to an HTTP URL:

(setq browse-url-filename-alist
'(("/webmaster@webserver:/home/www/html/" .
("^/\(ftp@\|anonymous@\)?\([^:]+\):/*" . "ftp://\2/")
("^/\([^:@]+@\)?\([^:]+\):/*" . "ftp://\1\2/")
("^/+" . "file:/")))

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.1 of Emacs.