On Linux: I am getting an error: Can't connect to X11 window server using ':0.0' as the value of the DISPLAY variable.

See here.

While sending an Email I am getting the error: ClassNotFoundException: javax/activation/DataSource

copy the file activation.jar to <jre>/lib/ext/

Changes are not correctly displayed in the browser

The browser or your http proxy is caching http data. Disable caching and reload the page into the browser with <shift>update (on most browsers)