My current favorite way to share my Kynetx apps is through Amazon’s S3. For Firefox to auto detect a Firefox extension and start the installation process, special Mime type headers need to be set. This can now be easily done with S3 through the AWS console or through a capable FTP client like cyberduck.
log into console and find extension file
Right click on file
Set content-type to application/x-xpinstall
Find file in cyberduck
Right click and select info or be cool and use the keyboard shortcut ‘cmd + i’
Set content-type to application/x-xpinstall in Metadata tab
For Google Chrome extensions, check out the documentation at http://code.google.com/chrome/extensions/hosting.html