I've been recently sporadically encountering an issue when posting comments. I write the comment, hit the ADD COMMENT button, and occasionally an image of a cat flashes and then a blank page is displayed in the browser, and a URL in the location bar that never finishes loading. When I reload, same thing (though not cat image). If I go back, the comment is gone.
Perhaps related, sometimes when I open new tabs on the SO site, the new tab seems not to know I'm logged in. A reload sometimes corrects that and sometimes not -- I occasionally have to log in again.
This did not used to happen, and the fact that nobody else has posted about it suggests it's something specific to my system. So, here are details:
WinXP Pro SP3 Firefox 3.6 (Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6)
The biggest change on my system recently is that I got rid of AVG antivirus (not the full suite, just the free AV) and started using MS Security Essentials.
If nobody else is encountering this, I'll chalk it up to interference by the latter.