This bug probably affects only the windows version of Mozilla.
The following two form elements are pre-filled with text containing non-breaking spaces. You can identify them in the hex dump as "a0" which is the iso-8859-1 code for .
0000 4e 6f 6e 2d 62 72 65 61 6b 69 6e 67 a0 53 70 61 Non-breaking·Spa
0010 63 65 73 20 4e 6f 6e 2d 62 72 65 61 6b 69 6e 67 ces Non-breaking
0020 a0 53 70 61 63 65 73 20 4e 6f 6e 2d 62 72 65 61 ·Spaces Non-brea
0030 6b 69 6e 67 a0 53 70 61 63 65 73 20 4e 6f 6e 2d king·Spaces Non-
0040 62 72 65 61 6b 69 6e 67 a0 53 70 61 63 65 73 20 breaking·Spaces
0050 4e 6f 6e 2d 62 72 65 61 6b 69 6e 67 a0 53 70 61 Non-breaking·Spa
0060 63 65 73 20 ces
0000 4e 6f 6e 2d 62 72 65 61 6b 69 6e 67 a0 53 70 61 Non-breaking·Spa
0010 63 65 73 20 4e 6f 6e 2d 62 72 65 61 6b 69 6e 67 ces Non-breaking
0020 a0 53 70 61 63 65 73 20 4e 6f 6e 2d 62 72 65 61 ·Spaces Non-brea
0030 6b 69 6e 67 a0 53 70 61 63 65 73 20 king·Spaces
[hidden input field]
0000 4e 6f 6e 2d 62 72 65 61 6b 69 6e 67 a0 53 70 61 Non-breaking·Spa
0010 63 65 73 20 4e 6f 6e 2d 62 72 65 61 6b 69 6e 67 ces Non-breaking
0020 a0 53 70 61 63 65 73 20 ·Spaces
When you hit the submit button below, the pre-filled text should be POSTed back to the server without any changes (unless you modify it manually, of course). You shall notice, however, that all (hex a0) are changed to ordinary spaces (hex 20), resulting in line breaks between the words "Non-breaking" and "Spaces" in the TEXTAREA element. Only the hidden field is handled correctly, so this is probably an issue with retrieving data from the edit controls.
Instead of using the pre-filled text, you can experiment with entering your own. s may be entered as Alt + 0160 on the numeric keypad.
Btw: IE6 gets this one right. Opera handles the TEXTAREA correctly, but fails on the single-line INPUT field.