Rendering of TIFF images broken
Since FAL was introduced in 6.0 the rendering of TIFF images seems to have been broken. This is due to the fact that the image processing is not converting the TIFF image to a web supported format. I've checked in version 4.7 and there TIFF images and probably other non web supported formats are converted to PNG. The problem goes even further than not converting it to the correct format, since it actually creates a cropped file and then renames that to a new file name with a wrong file extension.
The problem is a combination of things in "TYPO3\CMS\Core\Resource\Processing\LocalCropScaleMaskHelper" (#79) which creates the configuration sent to "TYPO3\\CMS\\Frontend\\Imaging\\GifBuilder", "TYPO3\CMS\Core\Resource\Processing\AbstractGraphicalTask" which hardcodes the target file name extension to "jpg" or "png" (#62) and "TYPO3\CMS\Core\Resource\Processing\LocalImageProcessor" which renames the processed file to the new target filename (#84).