Clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

See also:

• http://kb.mozillazine.org/The_page_is_not_redirecting_properly

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

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

As I said, I have already cleared YouTube's cookies, as well as the cache, and that didn't work. However, I will now check to see if it's one of my plug-ins, though I have very few active.

Also make sure that your security software isn't blocking cookies or the connection.

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

If clearing cookies didn't help then it is possible that the cookies.sqlite file that stores the cookies got corrupted.

• Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookies files like cookies.sqlite-journal in the Firefox profile folder in case the file cookies.sqlite got corrupted.

• http://kb.mozillazine.org/Cookies
• https://support.mozilla.org/kb/Deleting+cookies

Deleted the cookies files. Still doesn't seem to work. Didn't seem to be a problem with any plug-ins, either. Gonna try my security software now.

Also, I just tried logging in with a different account, and it worked (I had to log out of Google first in order to be able to log in with a different account).

For some reason, my main account is the only one that seems to be causing the issue. Not sure why my main account is causing Firefox to go into a loop, but my other account isn't.

YouTube still not working on that specific account. Starting to give up at this point. :/

EDIT: It started working again. I am honestly not sure what happened, but now I don't have issue anymore. It happened only with one of my accounts, but eventually it seemed to sort itself out after 48 hours or so. I really wish I knew what caused it and how it was fixed.