What Modx version are you using ??
I always leave the prefix empty and the result is as follows:
Say you homepage is called home and you have the doc alias as home, if the prefix is empty then the url would be www.yoursite.com/home.html
The above has been the same upto version 1.01 but I dont think it’s been changed in 1.02
Also how are you calling the pages in the links ??
If your using index.php?id=12 then it will always be that, you need to have your links as <a href="[~12~]">Home</a> ( that’s if it’s hard coded, if your using wayfinder this will be automatic )
And lastly make sure you clear the site cache
Yes, as far as im aware the preview doesn’t use friendly url’s as the .htaccess file for the main site and the manager are different.
Once viewed in the front end the .htaccess is engaged and the url’s are rendered as friendly url’s
EDIT:
Just to add as well, the reason for this is that the search engines cant access the manager or preview so there’s no reason for them to have friendly url’s
Thank you so much for your help, Paul. Problem solved!!