Third party profile backup software and services
From MozillaZine Knowledge Base
Only add-ons and programs that have been suggested several times in the forums are listed.
Ezbackup Ultimate and Thunderbird Backup are commercial programs to back up a profile to a directory, CD/DVD, or FTP server, and schedule an automated backup. The latter also has a freeware version that supposedly "has no functional or time limited restrictions compared to the full version".
Automated online backup
Mozy, BackBlaze , CrashPlan, Carbonite and Idrive are the most well known commercial services for automated online backup of files. Mozy is the most frequently recommended, and has a free version that provides 2GB of online storage. IDrive has a free version that provides 5GB of online storage.
In order to use the service you have to install client software that you can configure to periodically, automatically back up any modified files to the online storage they provide. Mozilla applications typically write to several configuration files (for example prefs.js) when exiting to guarantee that the file is in sync with what's in memory, even if nothing has changed. If the backup software just checks whether the time/date stamp has changed, it will unnecessarily back up those files.
If you're using SeaMonkey or Thunderbird you should consider telling it to exclude any *.msf files. Those files can be recreated by SeaMonkey and Thunderbird. You should also consider avoiding very large folders - split them into multiple folders. The backup software is smart enough not to back up a mbox file (the file used to store all of the messages in a specific folder) if it's already backed up, but its not smart enough to only upload the changes to a file. For example, if you move a 10KB new message to a 1GB folder it will back up the entire 1GB file.
Online file storage
Box.net , DropBox, FlipDrive and Microsoft OneDrive provide free password protected file storage, but no automated backup. How you back up your profile depends upon how they integrate uploading. Amazon Simple Storage Service (S3), ElephantDrive, JungleDisk and SugarSync are some other alternatives, though they don't have any free plans.
There are also some unusual hybrids such as Backupify. It will automatically backup Gmail, Hotmail and various social media such as Facebook, Flickr, Google Docs, Picasa, Twitter, Zoho, Blogger and Wordpress. They have a free personal account that can store up to 2GB plus various commercial plans.
One factor to consider when choosing online file storage is whether they're likely to go out of business, and if they do, how much time do you have to move your files. Xdrive has gone out of business twice already.
How Dropbox sacrifices user privacy for cost savings describes how DropBox only stores one copy of a file if several users upload the identical file (deduplication), and explains the privacy implications of this. When a online service encrypts your uploaded file that provides security, but doesn't necessarily provide privacy.