I exported my Firefox history from one computer using one operating system, then tried Importing the history file on another computer in another operating system and nothing happens after selecting the file. It only weighs about 27MB, so I don't think it's chugging behind the scenes.

I have a profile from a previous browser and have uploaded that places.sqlite file into your extension. It appears in my downloads folder as data.json. My history has not appeared in my browser. I closed/reopened firefox. Refreshed firefox. Still nothing. Can you provide further instructions on how to load this json file into the new browser?