When You are writing a lot in web forms e.g. issue tracker You definitely want a spellchecker enabled.
In Firefox You can do this via a config value.
- Type “about:config” into navigation bar
- Accept the “I will be careful” reminder
- Search for “layout.spellcheckDefault”
- Double click on entry
- Set value to 2
This will enable the spellchecker for multi-line controls and single-line controls.