Follow the below steps to configure this at the user's end but the user needs to be an Administrator to do so.
1) Start the Administration Manager (Spotfire Analyst > Tools menu > Administration Manager).
2) Select the Preferences tab.
3) Select a group on left pane. Use the Everyone group to set this for all users.
4) Click the Edit button in the lower right corner to edit preferences.
5) Expand TextArea > TextAreaPreferences.
6) Set the 'PerformHtmlSanitation' preference to 'False' to disable the HTML Sanitizer function.
7) Click the OK button to save values. Relaunch the Spotfire Analyst.