This has been happening for the last several Firefox updates, and it's an incredibly frustrating issue that makes me not want to ever exit the browser or update it. I'm not sure when or why exactly it started happening, but I believe it was after an update at least 3+ months ago. For some reason, when the browser opens from having been closed due to restart or update etc, and it restores my prior browsing session - it only ever restores 3 pinned tab as pinned. For some reason, it's always specifically just 3 tabs, and it's usually whatever the first 3 pinned tabs were. I always have at least 10 pinned tabs open due to the nature of my job. The tabs that are no longer pinned are restored in what looks like a random order, mixed in with my other tabs. Also, other tabs that weren't pinned, are restored out of order. This makes it difficult to find a tab and get it back to the order it should be in. I always just have a single window open. There are many tabs open as I work with a lot of cloud software at the same time. i have tried starting a whole new session from scratch, even uninstalling and reinstalling the browser. Doesn't seem to help, the issue returns on every launch. This looks like a bug to me, but I didn't find anything on it.