Regularly not shipping critical Firefox security patches for months is the norm for the main F-Droid repository. Whether or not they sign the apps themselves as they do for the vast majority of apps, updates can be indefinitely delayed based on issues with their outdated infrastructure or their Debian-style downstream patches needing to be updated.
For the small subset signed by the app developers, many kinds of disagreements between F-Droid and developers will mean an end to receiving updates.