Since we can now view images in AVIF format with Firefox, and together with other mainstream web browsers AVIF become a portable image format, it would be great to make a screenshot directly in this format.
What's more, AVIF (and the proprietary HEIC) supports big tiled images like TIFF but this format is more flexible and allows both good compression ratio and fast decoding. I'd love to make a (lossless) full page screenshot and save it as one single image file of a much smaller file size than it is using PNG images.
I'm also an extension developer (of Screenshot2HTML) and I hope this new format is also added to the API `browser.tabs.captureTab()`. 😁