Comment 22 for bug 37828

As Vincent says, this bug is not an Ubuntu only bug. It is just easier to hit on Ubuntu Dapper than other systems.

The prerequisites are:
 1. A Firefox build with pango enabled.
 2. Pango 1.12, which is the first version to use OpenType tables for
    rendering latin text.
 3. A font that contains OpenType ligature table entries, such as DejaVu (the
    Bitstream Vera fonts contain some ligature glyphs but not the associated
    OpenType tables that trigger their use by Pango).

The bug will then present itself on pages where the following hold:
 1. The page requests one of the affected fonts (if an affected font is the
    default serif or sans serif font, then this can be quite common).
 2. The page must trigger the slow manual glyph placement code path, which
    is used in the presence of non-default character or word spacing. The
    "text-align: justify" CSS rule is one way to do this.

The bug has been observed with Firefox 1.5.0.1. In the Launchpad bug, one person posted a screenshot showing that Firefox 1.6a1 did not seem to be affected by the bug. I have not verified this personally though.