Diễn đàn hỗ trợ Firefox

I have lost my tabs after the recent update. They used to show all tab groups in toolbar icon as mentioned here (https://support.mozilla.org/en-US/kb/tab-groups) in manage tabs section. Only the groups that were open are retained, the groups which were closed are lost. They contained important tabs which I haven't bookmarked. I didn't see any policy of removal of inactive tab groups after certain time, any help would be really appreciated. I use the desktop app on Linux.