This is how a web page fragment shows on my old 11.04 system:
and this is how the same fragment showed on 11.10 and shows on my current 12.04 system:
Any idea what's wrong? Of course I have all the same fonts installed (I believe the page uses some kind of Arial, which I installed from the mscorefontstt package IIRC) and I'm running the same version of Firefox. How can I fix things?
The right double parenthesis character (U+2E29) in your example appears in a few fonts only, according to a usually reliable (thought not quite complete) source: http://www.fileformat.info/info/unicode/char/2e29/fontsupport.htm
So the 12.04 rendering is what I would expect: it looks like a “missing glyph” indicator constructed by a browser. Presumably it was previously rendered using one of the rare fonts containing the character, a font that was somehow lost (e.g., moved somewhere where Firefox cannot find it). But Arial surely does not contain this character (which was introduced in Unicode 5.1, and Arial is much older).