I had the same problem. I have a triple boot system ( Win10, Kubuntu and Linux Mint ). It happened the same time on both Linux based systems. Lucky for me I could still get in my FF-account running on my Windows10. I exported the passwords as a .csv. Then I could boot my Kubuntu OS again, open FF and import the passwords there. Not all my passwords were there, because there are sites I don't visit in Windows, like the Linux forums. However my mail and other things I could recover. I learned to save/export my to a place which isn't accesable for FF during its install. First you can search for a .csv file if you exported your passwords before. Go to the three stripes icon in the taskbar, click on passwords. Then click on the three dots. If you don't see Import from a File… in the Firefox Lockwise menu, it means the feature is currently disabled. To enable it, go to the Firefox Configuration Editor (about:config page), find the signon.management.page.fileImport.enabled preference and toggle it to true. If the key is not there, make it. I hope this will help you. If not now I hope you learned something for the future. Good Luck.