SCLS is currently updating SCLS Network computers with the latest stable version of Mozilla Thunderbird (read more). The new version doesn't radically change many features so much as it brings the HTML rendering piece into line with emerging HTML5 techniques. As a side effect, the visual style of Thunderbird windows, menus and so forth is changing even though the features are much the same.
If you're like me, you may not like the new default display theme. The good news is that you can easily change it, just like you can change a Firefox persona or theme. The bad news is that a lot of themes that do work with Firefox are not compatible with Thunderbird, meaning there are not nearly as many choices.
The best options are listed here on the mozilla.org web site: https://addons.mozilla.org/en-US/thunderbird/themes/. My current favorite is Office Black; it's simple, effective, and seems to be well-maintained. Silvermel is also very nice but sometimes lags behind new TB versions.
To install a Thunderbird display theme:
1. Find a theme you like on the addons.mozilla.org website.
2. Download and save the theme as a file on your disk.
3. Open Thunderbird and choose Add-ons from the Tools menu.
4. Locate the Options button (looks like a cogwheel). It's next to the Add-ons search field.
5. Click the Options button and choose "Install Add-on From File".
6. Select the theme file you saved in step 2.
7. Restart Thunderbird.