Windows/Mac/Linux: Folders and labels in Thunderbird are great for at keeping your mail organised and out of your inbox, but they all look alike. Color Folders is a simple add-on that lets you customise the folders in Thunderbird however you like -- by priority, to match your Gmail labels, or just according to your tastes.
The add-on is simple enough -- install it from Mozilla Add-Ons, and you can right-click on any folder, select "ColorFolders", and set a colour for that folder. There's a small group of default colours, and you can click "More Colours" to see a broader palette to choose from. How you use the colours is up to you -- you can use them to highlight important folders, or you can use them to match you Gmail labels. You could also use them to just make a few folders stand out, like order confirmations or account notifications.
Whatever approach you choose, it's a simple tool that can go a long way towards making your inbox a bit more organised. If you're looking for more powerful extensions to try, check out our list of the best plugins to supercharge Thunderbird.