Symptoms

Unable to Browse Users in JIRA including:

• User Picker icons are greyed out and the link is inactive
  
• No suggestions are returned when attempting to add Watchers to an Issue.
  

Cause

The Global Permission 'Browse Users' is required for the above to work properly.

Resolution

• Assign the Global Permission 'Browse Users' to the appropriate groups in JIRA.

  See more details here on managing Global Permissions in JIRA: Global Permissions