Firefox ships by default with a spell check dictionary that matches the language version of the browser.
If you download the US version of Firefox, you’ll end up with the US English dictionary, for example. This usually works out of the box, but can sometimes be buggy. You can check out Fix Firefox Spell Check Not Working to fix potential spell checking issues.
Some users may want to have multiple dictionaries at their disposal, for example, if they have to write or spell-check US English and British English articles on the web, or if they communicate in at least two languages.
How do you do that? Additional dictionaries are added as plugins to the web browser. Many dictionaries and language packs are available on the Language Tools page in Mozilla. Simply visit the website and click the Install dictionary link next to the language you want to add to the Firefox web browser.
While that adds the dictionary for the selected language to the browser, it doesn’t add a means to quickly switch between dictionaries in Firefox. You see, Firefox can only load one dictionary file at a time, which means you have to manually switch between dictionaries every time you switch languages.
You can switch between spell check dictionaries with a right click on any web form that is displayed on at least two lines. You can then select languages from the context menu and switch to an already installed dictionary or select Add Dictionary to install a new one (which opens the same page linked above).
Maybe you want spell checking and dictionary switching to work on all forms, regardless of type. You can configure the browser to do that.
Get into about: config in the Firefox address bar and press the get into key after. New users must accept the warning. now come in layout.spellcheckDefault in the form at the top, double click the parameter of the same name and change it from the default value of 1 to two. The change is immediate and you should now see the spell checker and language context menu entry on all forms.
Having to switch dictionaries manually is a tedious task, especially if you have to switch on a regular basis. Enter the Add dictionary switch. It detects the language of the current page automatically and changes the dictionary if necessary. The plugin also adds an entry to the Firefox status bar that can be used to switch dictionaries with a single click and save the dictionary information for the current site so that the plugin does not have to scan the page again on future visits. .