While you appear to have a Firefox 115 version installed. You need Fx 115.13.0esr at minimum to not have Extensions be disabled and the current version is Fx 115.21.0esr and will be updated till 115.27.0esr in August unless Mozilla extends updates again. Are you using a package build of Firefox 115 as I know for example Debian Buster is EOL with package updates and the last Firefox package update was 115.12.0esr. If you cannot update your Firefox in your updates package manager then you can try the Firefox tarball archive from https://www.mozilla.org/firefox/all/desktop-esr/ as just run the Firefox script or Firefox-bin to start Firefox is the basics. This kb article explains in detail why the extensions are disabled in Firefox versions that does not meet the minimum. https://support.mozilla.org/en-US/kb/root-certificate-expiration