From MozillaZine Knowledge Base
The chrome folder contains files for customizing the application with CSS, userChrome.css and userContent.css. In Mozilla Suite and SeaMonkey 1.x, the chrome folder contains "chrome.rdf" overlays.rdf" and "*.jar" files related to added extensions and themes.
In Firefox and Thunderbird, this folder can be moved to a different profile without any extra effort.
Deleting this folder will cause the loss of any CSS customizations applied. In Mozilla Suite and SeaMonkey 1.x, deleting the chrome folder will cause the loss of any added extensions and themes.
Related files and folders