שלום חבר

שָׁלוֹם חָבֵר

With the correct font installed, the two Hebrew lines above should appear identical. This is the case on Windows using Firefox (50.0.2) and Chrome and IE, and on Linux using Chromium. It is also the case for word processing programs (MS Word and Office Libre Writer) on both systems. However, Firefox 52.0 on Linux (Ubuntu 16.04LTS) does not get it right.

The font which I used to demonstrate the problem is Stam Ashkenaz CLM, available as part of the culmus package on debian systems, or by direct download. (I am uncertain whether its license allows use as a web-font.) The difference between the two texts is that the first does not use diacritics (a.k.a. niqqud a.k.a. vowels), but the second one does. The font codes all Hebrew diacritics as "transparent", so the text should display normally without the diacritics. The problem is not restricted to the font I've used – it seems common to all fonts with such transparent characters. As stated above, this is handled correctly on Windows using Firefox (50.0.2) and Chrome and IE11, and on Linux (Ubuntu 16.04LTS) using Chromium. However, FF (52.0) goes to the fallback font for the diacritics on the same Linux system where Chromium succeeded, and so the vowels wind up being incorrectly displayed there.

For reference, I am attaching an image of the correct display:
Correctly displayed text
And an image of the incorrect display:
Correctly displayed text