ServiceNow icons are not visible in IE11 (Win7 + Win10) due to blocked web fonts

Description

A common security setting for Internet Explorer is to block web fonts from downloading. This conflicts with ServiceNow icons delivered via web fonts.

Custom web fonts such as 'SourceSansPro' and 'retina_icons' are used within the ServiceNow interface. So, if web fonts are blocked from downloading, substitute fonts may be used, and icons may not be visible in the UI.

Even if a local copy of these fonts exist on a user's machine, these local fonts will not be used by Internet Explorer 11. This is the case across all versions of Windows.

Currently, whenever the 'Source Sans Pro' font is used a fallback font seems to always be defined and so that will be used instead, minimizing the impact (as the text is still visible, but in the wrong font)
font-family: SourceSansPro, "Helvetica Neue", Arial;

However, in the case of the 'retina_icons' font, a fallback font cannot be defined because these are custom icon resources that are ServiceNow version specific.

Steps to Reproduce

1) Login an instance from a Windows 7 computer/virtual machine using Internet Explorer 11

2) In Internet Explorer, press the 'Tools' cog and choose 'Internet Options'

3) Choose the Security tab

4) With the 'Internet' zone selected, choose 'Custom level...'

5) In the list, find 'Downloads' > 'Font download' and set it to 'Disable'

6) Log on to the ServiceNow instance

Observe the text renders in 'Arial' font, and no icons in the interface appear.

Workaround

This issue has been identified as a possible future product enhancement. After carefully considering the severity and frequency of the issue, and the cost and risk of attempting a fix, it has been decided to not address this issue in any current or near future releases. We do not make these decisions lightly, and we apologize for any inconvenience.