I've solved it this way...
1) Create an override folder (if not existing) in your template folder for the Contact Form add-on. Copy the content from
2) In the admin.php file add the following code after '...
Firstly, I'll just point out that behavior.tooltip which is based on the JHtmlBehavior class, is old and deprecated, so I will base my answer on the newer Bootstrap tooltips.
Take the following HTML markup:
<a href="#" title="The text for the tooltip">Some link</a>
You can then utilise the JHtmlBootstrap class method, like so:
As your problem is not really with Joomla but with Docker and PHP this is probably not the best area to be asking about this issue.
A quick google search with 'stackexchange docker php' came up a few potential causes for your issue from some compression libraries not install by default to instruction for how you need to set up your Docker environment.
You seem to be on the right track.
Using the free or paid version of Sourcerer, you can build the link with the email address of the currently logged in user as follows:
$user = JFactory::getUser();
echo "<a href='http://www.othersystem.com/preprocess.php?em=" . $user->email . "'>Login</a>";
If there is ...