Ni one should be uploading tiffs for the general public unless it's an image file.
Tiff can be uncompressed or compressed, LZW.
A tiff can also be flat or layered. If layered and your image editing app is basic / rudimentary it wont understand the layers.
There is also a byte order for Windows vs OSX although that really makes no difference anymore. It really has to do more with OS specific apps than the OS.
Tiff is not a format that browsers can display.
I doubt that the images were loaded as tiff by mistake. I can see one or two as an accident but if everything is a tiff then they had a reason, like the files are layered.
Get yourself a copy of The GIMP.
GIMP - The GNU Image Manipulation Program
Free open source cross platform alternative to Photoshop.