I just wanted to add that I did a clean install (2.3.3) in the root and would get this error on both IE and FF.
I tried all the fixes and they would not work.
I then saw something about the config.php and that was my problem. I had strange characters at the start of the file. Once I removed them all was working.
I think that for some people this might be a red herring. If you are having problems even after fixes have a look at your config.php and make sure that it is ok.
