Navigation panel icons are broken if custom fonts are not allowed in Firefox

Feedback & Bug Reports
1

In Firefox 47, without any addons or tweaks, when you de-select “allow pages to choose their own fonts”, the icons on the sidebar are broken.

Some non-sidebar icons, like Github and Bitbucket ones, seems to be unaffected, even when they are made using fonts too.

There is a related discussion at https://bugzilla.mozilla.org/show_bug.cgi?id=789788 and it’s marked as fixed - as far as I understand, the icons that are done with characters from Unicode Private Use Area are all right:

Firefox default fonts are used but webfonts are allowed when
they contain characters not covered by the users default fonts (like icons)
(Comment 143 in that discussion)

2

I was not allowed to include more images in the post as a new user, so, here is where it’s set up in firefox:

Screenshot_20160815_152706.png634×523 32.2 KB

This dialog lives under Preferences -> Content tab -> Fonts section -> Advanced button.

3

Icons in help popup are working all right too.

4

Linux and OS X icons are unaffected as well.

5

Project Settings icon seems to be not working too.

6

Icon for closing notification is affected too.

Screenshot_20160815_163231.png760×58 2.43 KB

7

Builds summary page has some affected icons too:

8

SSH key management section has yet another affected icon.

9

I’m seeing this with Firefox 48 on Linux too. It’s quite annoying.