I don't think the issue you described is actually related to the extension itself, especially since you mentioned it only happens after the browser has been running for a long time.

When the extension is opened, it requests the list of bookmarks for the currently active folder only once. It's unlikely that the browser's bookmarks API, which provides that list, is the bottleneck. And even if it is, that's outside of the extension's control.

If your folder contains thousands (or even tens of thousands) of bookmarks and you're using a relatively modest computer, then yes, the browser API may take longer to return the list. However, at that point my extension is probably not the best tool for the job anyway. Rendering thousands of bookmark cards and keeping them interactive will inevitably lead to performance issues.

If you really have thousands of bookmarks in a single folder, I'd recommend using an extension that displays them as a simple text list instead.