When a rich text field's web edit property is marked "Best Fit For OS", the web server selects one of the HTML editors based on the browser.
The Java Applet is used for all browsers but Internet Explorer (IE). For internet explorer a combination of IE version and OS version (of the clinet) is used to choose the Applet (very old IE), the DHTML control or the (dojo) Javascript editor. (The latter for Vista and beyond, because the DHTML control is not available)
As of 8.5.1 FP1 the
domino-data-directory/browser.cnf file can be used to control the Best Fit For OS
to use dojo on more browsers, you can modify the browser.cnf rule for "RTEditorBestFit".
For example the following will allow the dojo control to be used by all browsers when a
field has been designated "Best Fit For OS"
Property RTEditorBestFit String Legacy
Rule JSControl MSIE [6-9].* Windows NT [6-9]
Rule JSControl Firefox/[3-9]
Rule JSControl Version/[3-9][0-9\.]* Safari
Rule JSControl Chrome/[2-9]