Ctrl+. / 
+.
(in the Main window hold
down the Control/
key and press the fullstop key). if you don’t like the results
you can undo them.
“Mr” (without a dot) is standard in the UK and
“Mr.” (with a dot) is standard in the USA (ref: Longman
Guide to English Usage 1988). In the interests of international
relations you can toggle between the two by using the
Ctrl+. / +.
(in the Main window hold
down the Control/
key and press the fullstop key). if you don’t like the results
you can undo them.
If you want to use “Mr.” (with a dot) as standard you should edit the titles available in the Titles tab of the Preferences window.