If you mean the interface, it may be simplest to install an English language version of the browser. Otherwise, you can install an English language pack. If you want to use English for spellchecking, you need to install an English dictionary if your chosen version doesn't contain one.

https://support.mozilla.org/en-US/kb/how-install-firefox-windows https://www.mozilla.org/firefox/all/#product-desktop-release https://addons.mozilla.org/firefox/language-tools/

You can try "Clear the startup cache..." via the "Help -> More Troubleshooting Information" (about:support) page.

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox

Can you attach a screenshot?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot