How to configure browser used by web page Reminders?
My results from user edgarator’s solution: Successful for macOS Safari users

Summary


Chrome icon changed to Safari after CleanMyMac Chrome Uninstall
Chrome icon appears again after Chrome is reinstalled
Removing files individually still had the Chrome icon, resulting in “no effect”
Firefox will open Reminders URL’s if it is set as the default web browser.
Firefox can’t share websites to Reminders. 
Firefox can’t use Siri to send websites to Reminders. 


Software Versions


macOS Sierra:         10.12.6
Apple Reminders:      4.0 (441.11)
CleanMyMac:           1.10.4
Google Chrome:        61.0.3163.79 (Official Build) (64-bit)
Safari:               10.1.2 (12603.3.8)
Firefox:              55.0.3 (64-bit)


My Process

Safari’s has a share website to Reminders feature (Share-to-Reminders).  Details can be added to a website reminder that is being sent to Reminders without leaving the browser.  

Now the problem: The shared links in Reminders uses Chrome icons which open Reminders items in Chrome, instead of Safari—or a designated browser.

I used CleanMyMac to uninstall Google Chrome, it's folders, and files.

After uninstalling Chrome, it's icon was replaced by Safari’s icon, pressing on the icon opened the link in Safari.

I then changed the default web browser to Firefox.  

Clicking on the URL’s directly, or Control-clicking the URL’s in the Info Pane, opens the link in Firefox (default browser).  

However, Firefox does not support Share-to-Reminders, so websites can’t be shared to Reminders from Firefox.  This also means that Siri does not execute the Share-to-Reminders command while using Firefox.