Paint me blind if you wish, but in bookmarks manager or in general preferences I couldn't find any option to import bookmarks in any format. Googling by keywords otter browser "import bookmarks" didn't help.
I have a large exported bookmarks file from Firefox in html nad json formats, and see no way to add the bookmarks to Otter. This is Otter version 0.9.99 weekly RC 12. Thank you.
