For Chrome
Click Settings.
Click Advanced.
Click Languages.
Under "Languages" slide "Spell check" to "On".
For Firefox
Click Options.
Under "Language" check "Check your spelling as you type".
For Microsoft Edge
Click start or press the Windows key, then type Settings.
Navigate to Devices and click on Typing on the left pane.
Under Spelling, turn on "Highlight misspelled words".
For Safari
If necessary, first click "Settings" and then "Show Menu Bar"
Click Edit.
Click Spelling & Grammar.
Click Check Spelling While Typing.