The screen shots below illustrate comments that displayed error-free before I clicked Add/Show Comments and with problems (text overwriting causing illegibility) after I clicked it. Can the bug be fixed?
This might be related to question 84626 where platform but not site-dependency was mentioned as a possible source for the error.
For sites I tested on, the error occurs on stackoverflow.com, meta.stackoverflow.com, and serverfault.com and the error does not occur on english.stackexchange.com, math.stackexchange.com, programmers.stackexchange.com, and writers.stackexchange.com.
Illustrations of the problem are from SO question 8012458, from browser Firefox 3.6.22
on linux 126.96.36.199-96.fc14.i686. In the browser, default font size is 18 and the box for "Allow pages to choose their own font, instead of my selections above" is checked. Using the mouse scroll wheel to change font size does not affect the amount of text overlap. As a workaround, if I decide to read the comments I highlight right sidebar text, right click, and delete selection (via Nuke Anything addon).
Edit 1: Enabling/disabling Adblock Plus addon has no effect on the problem; it occurs with either setting.