We've released free updates to Image Rotator Magic and Slide Show Magic which address occasional flickering in Firefox 3.6 and Firefox 4.0. The flickering was traced to Firefox javascript engine bugs. Please follow the insructions on the update pages:
http://www.projectseven.com/support/updatepages/irm.htm
http://www.projectseven.com/support/updatepages/ssm.htm
You'll need to download the updates, install them, and then update the IRM and/or SSM script file linked to your page(s).
Don't skip any steps :-)