It seems like for at least a couple of years now, I've had problems when trying to login to newegg.com with Firefox. Across different installs of Firefox, on Windows, OS X, and Linux, etc.. no matter what I tried, Firefox just didn't work at all. Today after my typical google search session, I did find a couple of solutions which took quite awhile to track down. If you're having problems logging into to Newegg, give these a try:

Easy solution:

In the address bar of Firefox, type:

PLAIN TEXT
CODE:
  1. about:config

Search or scroll down to the section called "network.http.sendRefererHeader" and change this value to 1.

For some reason, this was set to 2 on my machine.

Annoying solution:

Something is probably corrupt in your Firefox profile. Given that you're the type of person who shops at newegg, AND uses firefox, you can probably figure out how to create a new profile on your own.

Anyhow, give those a try and see if they work. It's nice to be able to shop on Newegg again with Firefox!