Although BirdieSync has been heavily tested, it is strongly recommended to backup your data before installing a new version.
All your contacts, events, tasks and emails are stored in Thunderbird profile directory. It is recommended to regularly backup this directory.
In recent versions of Thunderbird, you may find your profile directory with Thunderbird menu "Help / Troubleshooting information", "Profile folder" entry (click on "Open folder")
Otherwise you may manually access to your Profile directory from Windows Explorer:
XP: C:\Documents and Settings\[users name]\Application Data\Thunderbird\Profiles\
Vista - Windows 10: C:\Users\[user name]\AppData\Roaming\Thunderbird\Profiles\
(Application Data and AppData are hidden folders: in explorer window, you must check the option "Show hidden files and folders")
To backup your mobile device, here are some examples of applications you may use: