I downloaded SRFR yesterday and tried to use the 'Modul Class Suffix'. The module ignored the suffix. I check the CSS output and found a bug the default.php files in both module templates (default & compact).

I delete in the default.php file/s located in modules/mod_sw_srfr/tmpl/default/ (and /compact/) an unnecessary blank in line 43:

Given: <div class="srfrContainer <?php echo $moduleclass_sfx; ?>">

New: <div class="srfrContainer<?php echo $moduleclass_sfx; ?>">

This fix it for me.

Please understand this as thank for your great module - simple but effective.
Perhaps other users have the same problem and my fix is helpful.  8)