How to Switching between HTTP and HTTPS in Joomla 3

To first force HTTPS in Joomla based sites, first you must check the correct environment variable %{HTTPS} off, but your rule above then prepends the www. Since you have a second rule to enforce www., don't use it in the first rule.

Rule 1:

# First rewrite to HTTPS:
# Don't put www. here. If it is already there it will be included, if not
# the subsequent rule will catch it.
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

Rule 2:

# Now, rewrite any request to the wrong domain to use www.
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ https://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]