Are that themes you installed from the Add-ons (AMO) website or built-in colorways themes ? *https://support.mozilla.org/en-US/kb/use-themes-change-look-of-firefox *https://support.mozilla.org/en-US/kb/personalize-firefox-colorways You can try to rename extensions.json (extensionsOLD.json) in the Firefox profile folder as that is where all add-ons are registered. Extension's XPI files are stored in the extensions folder. *https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Thanks this is how I deleted theme In the [https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data Firefox folder], there is a folder called extension in there you can find add-ons and themes witch i deleted all themes