Extension StickyFeed

Hello !

I've found a little bug in the Sticky Feeds extension. When using a web browser to access my FreshRSS installation, I can use Safari or Firefox :

### Safari / extension off
In this configuration, the left bar (feeds tree) scrolls out of sight with the content.

https://user-images.githubusercontent.com/46840243/147943483-979b172f-5415-4eef-95de-57bef9086f70.mov

### Safari / extension on
Here, the menu stay in place. I can scroll inside, or in the content on the right, independently.

https://user-images.githubusercontent.com/46840243/147943511-01351389-5335-4d48-803e-3e04829bd344.mov

### Firefox / extension off
The menu stay in place, I can scroll both part independently.

https://user-images.githubusercontent.com/46840243/147943526-c2891991-e6ae-413b-b804-17ba06b01835.mov

### Firefox / extension on
This is quite funny actually : when I scroll down on the content side, the feeds menu goes down out of screen entirely. 😂

https://user-images.githubusercontent.com/46840243/147943554-b75ee439-72ed-47ef-a485-45c9e9ec20f3.mov

So the 1) the behavior is not consistant between browser and extension status and 2) Firefox is going nuts when it's active.
Any idea ?

🖖