''I don't know about recovering/changing Windows passwords in Windows 10 on a personal system (my login is on a work system). A Windows forum probably would be better for that question.'' To recover Firefox data from the Windows user you can't log in under, if your working user account has administrator privileges, you can try grabbing those files this way: (1) Set Windows to show hidden files and folders https://support.microsoft.com/en-us/windows/show-hidden-files-0320fe58-0117-fd59-6851-9b7f9840fdb2 (2) Explore up this path C:\Users\''locked_user''\AppData\Roaming\Mozilla (3) Right-click the Firefox folder and click copy; Windows may require admin approval for the paste (4) On your working user desktop, right-click > Paste the folder; Windows may require admin approval for the paste (5) Right-click the pasted folder and click Rename, and add something like OLD or BACKUP or the other user name here for reference That folder should contain your key Firefox data from your other Windows user. Is there anything in particular you are looking for? Depending on your needs, either a selective or a wholesale restore might be the next thing to try.