Add a visual display showing if a filter is set, or not.
This would help avoiding this problem, where a filter setting was set to the linked references, but this was not visible without clicking on the filter icon: Inconsistent Linked References: Why Are Some Journal Page Mentions Not Appearing?
Agree. This would make for a really simple improvement - just add a red dot (e.g. the same way how it appears on the plugins icon when there’s an update available) to the filter icon when a filter is applied
As an additional related improvement, I’d suggest making the filter icon floating when scrolling through active references. This would make it easier to change filters when you realise you’re looking for the wrong related page