This is because only admins have privileges to check "Enable HTML code" in comments.
If you want to change it you must edit xoops/include/comment_form.php
In line 79,80,81 you'll see the following code:
$html_checkbox = new XoopsFormCheckBox('', 'dohtml', $dohtml);
$html_checkbox->addOption(1, _CM_DOHTML);
$option_tray->addElement($html_checkbox);
You need to move it out of the if clause, for example before line 85:
$smiley_checkbox = new XoopsFormCheckBox('', 'dosmiley', $dosmiley);
The resultant code will be like this:
}
}
$html_checkbox = new XoopsFormCheckBox('', 'dohtml', $dohtml);
$html_checkbox->addOption(1, _CM_DOHTML);
$option_tray->addElement($html_checkbox);
$smiley_checkbox = new XoopsFormCheckBox('', 'dosmiley', $dosmiley);
$smiley_checkbox->addOption(1, _CM_DOSMILEY);
...
But remember, you don't need to use the default toolbar with all buttons everywhere.
You can build your own or use the 'small' one:
$wysiwyg_text_area= new XoopsFormWysiwygTextArea( _MD_CONTENTC, 'content', $value, '100%', '400px','small');