Don't use powers of 1000 for ISO size on the download page

Originally created by @anonym on #9374 (Redmine)

Since #7417 (closed) we show the ISO image size on the download page, and it uses powers of 1000 and the unit “MB”, which is completely correct. But it risks confusing users, since reason lost this battle (at least so far) and an inconsistent use of the power vs unit is what users is likely to be exposed to. Here’s what I looked at to draw that conclusion:

• Firefox shows the number in MiB:s but incorrectly uses the unit “MB”
• Chromium/Google Chrome shows the number in MiB:s but incorrectly uses the unit “MB”
• Windows 8.1’s explorer shows the number in MiB:s but incorrectly uses the unit “MB”
• KDE’s Dolphin shows the number in MiB:s and correctly uses the unit “MiB”
• GNOME’s Nautilus shows the number in MB:s and correctly uses the unit “MB”

So, showing the number in MiB:s but incorrectly using the unit “MB” is what most users will be exposed to, in particular when downloading the file. The difference becomes very noticeable given our ISO image size, e.g. for Tails 1.4 its 971 MB vs 926 MiB (in correct units!). With the current situation users may think they are downloading a Tails containing 45 “MB” worth of NSA backdoors, or whatever.

Feature Branch: web/9374-iso-size-units

Related issues

• Related to #7417 (closed)
• Related to #15104 (closed)
• Blocks #9438 (closed)