Yes, in Firefox the 'esszet' is transformed in SS when in capital letters. But this done since a long time. The dotted and dot-less Turkic, and the Dutch IJ, are new in Firefox 14 (which is the first browser to support it, AFAIK).

There is some specific cases with accented Greek diphthongs, where the diacritic position changes in upper and lower case, but Mozilla is working on a fix.