I am trying to load tiff images using fiftyone and python in ipynb notebook, but it just doesn't work. Anyone knows how to do it?

The images types that FiftyOne supports are based on the underlying support of the browser you are using to run FiftyOne. TIFF is only supported out of the box by a few browsers like Safari: https://en.wikipedia.org/wiki/Comparison_of_web_browsers#Image_format_support

For other browsers, you will need to check if there is an extension that adds TIFF support, like this one for Firefox: https://addons.mozilla.org/en-US/firefox/addon/tiff-viewer/