Conditional field name selector not loading metrics in Firefox

[jescalada]

Small remaining issue from https://github.com/G-Research/fasttrackml-ui-aim/pull/86 which I've been seeing on Firefox:

Instead of loading the list of metrics, only "metrics.undefined" is shown. I suspect this has to do with some inconsistent state from previously running in development (and changing the way the conditions get stored). It seems to work fine in Chrome.