In my Selenium tests I want to upload some files. Due to security restrictions it is by default not possible that a Javascript fills in a path in the respective input field. But fortunately, there exists a workaround:

a) The Mozilla must have the configuration option
“signed.applets.codebase_principal_support” set to the value “true”.
This allows non-signed scripts to request higher privileges.

b) Selenium must request higher privileges which can be handled in
different places. To allow typing into file fields you can include this
call:

netscape.security.PrivilegeManager.enablePrivilege(”UniversalFileRead”);

in the file selenium-api.js in function Selenium.prototype.doType. This
enables uploading local files.

This workaround works also with Firefox.