Comment 71 for bug 228988

Assuming that in step 4 by "select" you meant double-click the word in red, I can't reproduce on Mac, neither using 3.6.12, nor using Firefox 4 nightlies.

This is the page that opens in a frame in the pop-up: http://194.214.124.200/dendien/scripts/tlfiv5/displayp.exe?18;s=atilf_40_2841007530;i=ft-4-2.htm;;
It doesn't send the charset in HTTP headers at all and doesn't specify the charset in the HTML, as far as I can see.

Can you reproduce using a clean profile? <http://support.mozilla.com/en-US/kb/Basic+Troubleshooting> With a build from mozilla.org? What's selected in View -> Character Encoding -> Autodetect?