In all the Windows versions have been through once it starts putting out diacritics. Things go bad. This is a Microsoft Issue am 90% sure of. So with send info to Mozilla turned off, i have no info... So Norwegian is your every day use I think. You have a Language pack installed for Firefox ? A Dictionary ? If so see if can update them from the Extensions Page. If you are running a Norwegian version of Firefox I am lost....... Are you running a Norwegian version of Win10 or just a language pack ? I suggest that you try the steps below and check if it helps. Remember how to reverse them....... On the Win10 search bar type “Control Panel” and then go to “Clock, Language and Region”. Click on “Language” and on the left pane, locate “Advance Settings” and click on it. Locate “Override on Default Input Method” click on the drop down box and choose your preferred language (English US).(What ever you want) Also make sure that “Override for windows display language” drop down box is set as English (US).(What ever you want) Click on “OK” and restart your system and check if it resolves your issue. If you want the input language (read and type) to be French or Italian, you need to download the language pack and by following the below steps. 1. In the search option of the taskbar type Region and language and press enter. 2. If you don’t have French or Italian languages, download them by selecting “Add a language” option. 3. After adding the language follow the step 1, select the language and click on “set as default”. Reference: Change your language or keyboard: http://windows.microsoft.com/en-in/windows-8/add-language-keyboard Add a keyboard layout: http://windows.microsoft.com/en-IN/windows-8/change-keyboard-layout This is going to get long............... Ok.......... Suggest this as will not harm a thing. Please uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. Reinstall with Current Release Firefox 57.0 with a Full Version Installer https://www.mozilla.org/firefox/all/ Choose Language. For Windows 10 Repair System Registry and Files (FOR DOING Above & Below - WINDOWS All OTHER VERSIONS - Use Search To Find Command Prompt ** Enter CMD.exe to Find COMMAND PROMPT Then Right Click & RUN AS ADMIN) To run the SFC command use the Windows key + X keyboard shortcut to open the Power User menu and select Command Prompt (Admin). Type "SFC /SCANNOW" (without quotes or copy/paste) and press Enter. For more information on using SFC, please refer to the Microsoft KB: Use the System File Checker tool to repair missing or corrupted system files Run the Windows Deployment Image Servicing and Management (DISM) and System File Checker (SFC) tools as Administrator. The DISM and SFC tools scan the integrity of the Windows image and all protected system files replaces corrupted, damaged and incorrect versions. (FOR DOING Above & Below - WINDOWS All OTHER VERSIONS - Use Search To Find Command Prompt ** Enter CMD.exe to Find COMMAND PROMPT Then Right Click & RUN AS ADMIN) Type "DISM /Online /Cleanup-Image /RestoreHealth" (without quotes or copy/paste) and press Enter. Windows 10 To run the DISM command use the Windows key + X keyboard shortcut to open the Power User menu, then select Command Prompt (Admin). Type "DISM /Online /Cleanup-Image /RestoreHealth" (without quotes or copy/paste) and press Enter. While running DISM you may notice the process will appear to pause at 20%. After a few minutes the operation will continue. Note : SFC fixes files locally using files found on your system. Note : DISM goes up to Microsoft for new ones. Please let us know if this solved your issue or if need further assistance.