It seems that your Form element for Select has a bug. When I first click on a select field to chose an option the select field does not actually open. There is a second click on the select field needed to get the full list of choices. I couldn't reporoduce this bug with the materializecss.com framework
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This issue occur only on FF and this is due to older framework, we are in process of releasing our next update including this fix in 2 weeks.
Please have patience.