In iOS 8, enabling the "Read Tiff" app extension is the easiest way to read a TIF/TIFF file in Safari.
To enable the Read Tiff app extension:
1) Navigate to a URL of a TIF/TIFF file in Safari.
2) Locate the Share icon (The box with the arrow) and tap it.
3) In the bottom row of icons, swipe until you're at the right-most end of the list. Tap More (...)
4) Enable the Read Tiff switch and tap Done.
5) You should now be able to see and use the Read Tiff app extension to read the TIFF file directly from Safari.