Script Summary: Rounds corners and adjusts appearance of textarea, select, button, and input fields. Resulting eye-candy is somewhat Safari-like. Applies globally, but you can exclude sites or apply it only to selected sites.
A corresponding Stylish script can be found at http://userstyles.org/styles/8986
A few minor tweaks regarding '!important' and colors so that the script is better behaved at being compatible with the dimensions and colors of buttons and form fields, where established by a particular site's CSS.
Version 1.10 (16-Apr-09)
Simplified greatly. Redesigned so that input, textarea, and select fields and buttons have dimensions identical to these items as defined in Firefox's 'forms.css' file. The styles are no longer all denoted as '!important' -- if a site has its own styles for these items, the site's style will override.
Version 1.06 (25-Jul-08)
Further minor tweaking (-1px) to input, select, and textarea fields.
Version 1.05 (23-Jul-08)
An "exception handling" section has been included to deal with peculiarities of the Firefox add-ons web site. Thanks to Joe Simmons at http://userscripts.org/users/23652 !!
Version 1.04 (23-Jul-08)
Slight (1px) modifications to input areas for slight aesthetic improvements. Also, some minor reorganization of script CSS components to make it easier to read and understand.
Version 1.03 (12-Jul-08)
Now with improved handling of 'select' (dropdown) tags.
Screenshots, before and after: