Update! the bug (triming items to just 5000 also seems to happen in firefox dev edition, I guess it had more items for some reason, but now syncing trims it back to 5000. Hope you can fix it (BTW i replied to your comment and sent you a message, but no response yet).

Original review:

This is wonderfull! Thank you very much for doing what Firefox themselves should have done since a lot of time now (they now own Pocket FYI)
But I found what seems to be a bug.

For some reason, if I use the extension in Waterfox (the fork of firefox that still supports several legacy extensions), anytime I sync my Pocket, the count badge "trims" at 5000 items, even if I have more. Now, if I add new items during that session, they add correctly, showing 5001, 5002, ... 5027 or whatever. It is only if I sync it via the button, that it resets to 5000.

I thought that it may have deleted my oldest items past 5000 (everytime I manually sync), but I checked in Firefox Developer edition and the badge count in there correctly shows my current (6454 at this moment) item count. I currently don't have regular firefox installed, but I assume the badge count shows correctly there.

I assume that for some reason, in Waterfox, it just fetches the most recent 5000 items, while in Firefox it fetches all of them.

Could you look into it! Thanks again!