Browsers and Devices
At the front end, our extensions produce valid HTML5 and CSS 3.0, which are now well supported by the vast majority of modern browsers and devices. We obviously can't guarantee perfect results on every device, especially older devices. If you find a rendering problem in a major browser on an important device, please contact us and we will try to find a solution.
We develop and test using PHP 5.3, 5.5 and 7 on Mac, Windows and Linux. We have PHP error reporting set to E_ALL | E_STRICT, which means that our released code should not issue any errors or notices. If you do see any errors or notices, please tell us and we will fix them. If you have not yet upgraded to PHP 7 you should start making plans to upgrade. Sites run noticeably faster with PHP 7, and Joomla 4 will require PHP 7 as a minimum.
Joomla has always supported MySql. Joomla 3 added support for SQL Server and PostgreSQL. Our extensions only support MySql. We develop and test using MySql 5.5 and 5.6.
Joomla 4 will drop support for SQL Server, and it seems likely that support for PostgreSQL will eventually be dropped. We have never received a single request for either SQL Server or PostgreSQL support.