Yt-bookmarks by Kirill Makarov

This add-on allows you to save and restore a video time position between sessions.
It adds a button with an orange bookmark sign on it to the toolbar.

If you want to save a time position, just click on the 'Save time' button.
If you want to restore last time you saved, click on the first (on the top) blue line.
If you forgot to save time or your browser crashed, you can restore time from the "Previous auto saves" section.

NOTE: The add-on does not distinguish between advertising and normal videos, so it can save wrong time during an advertising video.