Two-factor authentication is an optional security feature where sites require you to enter a code received by email or text message, or generated by an app. It doesn't sound relevant to me.

Does Firefox show any of the usual indications in the lower left corner such as connecting, reading, etc.?

During the waiting time, can you open another tab and get to other sites, or is Firefox just busy/distracted and not yet able to retrieve sites?

Is there anything special about your network settings, such as using a proxy, VPN, or DNS over HTTPS?

Here's a somewhat similar thread suggesting a Kaspersky settings override is a potential factor in causing delayed first page load: https://support.mozilla.org/questions/1271170

(note that the OP is using Linux)

See also:

• https://support.mozilla.org/en-US/kb/secure-firefox-account-two-step-authentication
• https://www.google.com/landing/2step/

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems