Here is the simple tutorial which you will find useful, to setup Xmark on Chrome as well as firefox.
In your Firefox browser go to Tools > Addons > Get Addons.
Search for Xmarks.
Click on Install button.
It will ask to restart your browser. Click on Restart.
Now go to Tools > Xmark > Xmark Setting
Click on Run Setup Wizard
In the Log in to Xmarks window click on Create an account for new account
Fill up the require details and click on Create Account button
Enter your computer name
If you want to synchronize your browser history click on Enable synchronization of browser history
Enable the appropriate options you want in next screen
Xmark will automatically start synchronizing your data.
After completing all the steps successfully you will get the success windows.
Now open Chrome Browser and install Xmark plugin.
After installation you will get Xmark icon on the right hand side of your browser.
In the Xmark setting window click on Run Setup Wizard
Click on Next button to start the configuration part
We will use the email@example.com account which we have created earlier to sync the the data. Click on Log me in radio option.
Fill require details.
It will check your login with their servers
Click on the Change Sync Setting button
I choose Merge bookmarks with server, starting with the server, as I also want to synchronize chorme bookmarks
Click on Sync Button, to start the synchronization.
After successful configuration it will show you merge complete message.
If you want to secure your data transmission you have to encrypt it. To do so go to Xmark Settings > Advanced and select Encryption to Encrypt All.