While fixing up the spell checker dictionary logic, it became clear that the spell checking dictionary check is case sensitive, which regularly doesn't work if websites have languages specified in lower case (a common occurrence). The spellchecker should make a case-insensitive check for language specified to match a dictionary to the element/document language. See also: See https://bugzilla.mozilla.org/show_bug.cgi?id=1073840#c34

Will be fixed as part of bug 1200533. Take a look at attachment 8656398 [details] [diff] [review], there we have now: // Before we start, let's correct any problems due to non-matching case. int32_t i, dictCount = dictList.Length(); for (i = 0; i < dictCount; i++) { nsAutoString dictStr(dictList.ElementAt(i)); if (dictName.Equals(dictStr, nsCaseInsensitiveStringComparator())) { dictName.Assign(dictStr); printf ("***** Corrected dictName to |%s|\n", NS_ConvertUTF16toUTF8(dictName).get()); break; } }

BTW the current behaviour is *incorrect* standards-wise. RFC 5646, section 2.1.1. Formatting of Language Tags At all times, language tags and their subtags, including private use and extensions, are to be treated as case insensitive: there exist conventions for the capitalization of some of the subtags, but these MUST NOT be taken to carry meaning. Thus, the tag "mn-Cyrl-MN" is not distinct from "MN-cYRL-mn" or "mN- cYrL-Mn" (or any other combination), and each of these variations conveys the same meaning: Mongolian written in the Cyrillic script as used in Mongolia. http://www.ietf.org/rfc/bcp/bcp47.txt RFC 1766, 2. The Language tag NOTE: The ISO 639/ISO 3166 convention is that language names are written in lower case, while country codes are written in upper case. This convention is recommended, but not enforced; the tags are case insensitive.

Good to know, thanks! We'll fix it.

Fixed as part of bug 1200533.