Blue Canvas allows you to quickly compare orgs to see what differences exist in your Profiles and Permission Sets. Read the docs.
Diff by Object & Field
You can filter by Object to see which Objects and Fields have different Profile and Permission Sets.
Our simple user interface is designed to make it easy for admins and developers alike to deploy Profiles and Permission Sets in Salesforce.
If you need to restore Permissions after the Pardot Reset
If your are affected by the Pardot permission reset, you can use this tool to restore permissions. You need to have access to a Sandbox that contains a valid backup of your Profiles and Permission Sets. Follow these steps:
Confirm that the Sandbox can be used to restore Profiles and Permission Sets.
Login to the Sandbox, open Setup, and go to Profiles. Open a regular Profile (not Salesforce Administrator) and look at the Standard Object Permissions. If Read, Create, Edit, Delete are unchecked, then the Sandbox was reset and can't be used in this restore. Try to find another Sandbox that wasn't reset.
If the Profiles on the Sandbox are intact, continue with the next steps.
Connect your Sandbox as the Source Org on the top right of this page. Log in with your administrator account when prompted. Then connect your Target Org.
Copy the missing permissions.
In the left sidebar, open Profiles and select the profile to restore. Select one profile at a time, and repeat this process for each one separately. If you select too many profiles at once, you will see a timeout.
In the left sidebar, open Object and Field Permissions and click Select All. Next, click the Compare button. Many permissions will appear. Select all of them by clicking the [+] button next to the profile name. In the right sidebar, click the Deploy button to restore the selected permissions.
If you have problems with managed permissions, you need to reinstall the managed package.
Install the package again. Don't uninstall the package.
This will not work if the current package version has been deprecated, or a newer version of the package has been installed and that version doesn't include the permissions. Try to find an older version in those cases.
You should repeat this process for every profile and org with missing permissions. After you're done, log in to the target org and check that the restore went as expected.