Just discovered it appears multi-select picklists are not working in Firefox 3.6.12. The picklist dialog comes up but when you click OK with your choices the picklist text box remains empty. The picklists work fine on IE. This is in SalesLogix 7.5.3.
Update: Thanks to Todd Hardin on this. Apparently in Firefox you need to set the max length of the picklist to a value other than 0.