Stylish 3.1.5 still sends full URLs for every website you visit. The interface is highly deceptive. Do NOT install this malicious extension, especially since there is a functionally equivalent add-on that respects your privacy: Stylus.
When opening the Stylish icon, a message with an opt-in request is shown followed by an “OK” button. It does not look like an opt-in request (“Agree” [with terms]) at all, but a notification (“OK” [to dismiss]):
Clicking “OK” silently enables tracking, this cannot really be considered consent I suppose.
Once the setting is enabled (after installation, through this pop-up or preferences), it will track all website visits again (exactly the same way as was done before in version 3.1.1). If you are curious, this is the data that is sent to the third party (userstylesapi dot com) for every webpage you visit:
As you can see, this report in fact contains very personal identifiable information. The option:
[ ] Send de-identified browsing data to Stylish to access style suggestions through the toolbar menu
is more accurately described by:
[ ] Send the full URL (possibly containing personal information) to Stylish. This enables style suggestions through the toolbar.
If you would like this company to know every website you visit (which may include your address, location, name, date of birth, family/friend/business connections, etc.), install this extension. Otherwise, you are better off uninstalling Stylish and warning your peers to stay away from this add-on.