It sounds like the issue is browser-specific. Here are some steps to resolve it:
Clear Cache and Cookies: Go to your browser settings, clear the cache and cookies, and try logging in again.
Disable Extensions: Temporarily disable any browser extensions, especially ad blockers or VPNs, that might interfere with the login process.
Check Browser Settings: Ensure JavaScript is enabled and that cookies are not being blocked.
Try Incognito Mode: Open the browser in incognito/private mode and attempt the login.
Update Your Browser: Make sure your browser is up to date with the latest version.
Switch Browsers: Since you can log in using Chrome and Edge, consider continuing with one of them until the issue is resolved.
If none of these steps work, contacting Xfinity support might provide additional insight.