Thunderbird would prompt you for a password in case it needs one. If it can't reach the server, it won't prompt you. Check your Internet connectivity. Also see https://support.mozilla.org/en-US/kb/problems-sending-and-receiving-messages

since i am using gmail for all 4 accounts, i can access them online (thro' a browser). Something seems to be wrong with the password since i don't see the passwords in the security settings. The "Password" tab is not high-lighted & therefore i cannot remove or add or edit any passwords.

Item 1. The ability to access gmail in a browser proves only one thing. You know the password. Nothing else.

Item 2. Your reference to the prefs.js file sounds like your reading instructions for Versions prior to 1 whewn the config editor was introduced.

Item 3. General internet browsing in done on ports 80 and 443 (SSL) Mail is done on Ports 110, 995, 143, 993, 25, 26,587 and 465. So being able to browse the internet does not mean that Thunderbird can get out there.

Item 4. Crist1 is correct that Thunderbird will ask for a password if it is required. The fact it is not indicates it is not even getting out to the internet.

Now the common reasons Gmail stops working are.

a) Two factor authentication is enabled at Googles behest but no application password is generated for Thunderbird. They forget to tell people that bit.

b) You do not have "access for less secure apps" enabled in your gmail profile.

c) IMAP or POP access has been disabled in the gmail profile.

d) Your anti virus is blocking mail because it has decided to. Disable email scanning or better still reboot into Windows safe mode with networking and see if it works then

e) Anti virus /Firewall is blocking Thunderbird or the ports needed to access mail.

f) New modem / Router / wifi extender that blocks ports that the old one did not.