While browsers have spellcheck enabled by default, it is possible to turn it off. Check your settings as below:
- Safari: Edit menu, Spelling and Grammar, Correct Spelling Automatically needs to be on.
- Chrome: Settings, Advanced, Languages, Language and input settings, Enable spell checking needs to be on.
- Firefox: Preferences, Advanced, General, Check my spelling as I type needs to be on.
- Edge and IE: Windows-I. Devices, Typing, Highlight misspelled words needs to be on.