My experience discussing fox on these and other boards is that lefties typically have never actually watched the channel itself but instead get their opinion from carefully selected youtube videos spoon-fed to them by other liberals who hate Fox and ensuring that they form the only opinion they're allowed to have about it as "good liberals". This is exactly the same way a "good conservatives" is only allowed to have one opinion of MSNBC, and that it must be run out of business because of its bias.
Generally the fox haters like to tell themselves that the increased ratings FNC receives is due to liberals who hate the channel watching it because its a "train wreck" whereas conservatives have it easy because MSNBC's ratings actually do suck.
As I've said before many many times here. Fox is no more biased than CNN, the BBC, or any other news channel out there. For the most part it is intellectually dishonest and selective outrage against the segment of the news that disagrees with their politics and nothing more (yes from both sides). They highlight mistakes that were made because the haters know that they are generally the only people obsessive enough to have video on hand and they won't have to acknowlege that every news source makes these mistakes in varying severities on literally a daily basis, but none significantly more than any other. Another group of folks has actually convinced themselves that they are capable of determining bias from non-bias and that their outlet is the best because they can determine it.
Anyone who thinks they are getting unbiased news and isn't getting it from their own perceptions is lying to themselves. FNC, MSNBC, CNN, AP, BBC, etc...all biased. Some just like to feel like they have "all the facts" so they convince themselves their source is the one special unbiased one. This is of course Naive (with a capital 'N') to say the least.