This worked for me a little differently.

I could not get microb to keep the settings. Whatever I tried, be it closing the browser before, rebooting before starting it again, the browser would just delete these lines on startup.

The following did work for me though. I opened a new browser window and typed "about:config" in the URL. The page that opened provided a way to add new lines to the configration. I added the entries from the post above and microb stopped asking for confirmation on save.