Even though what callahan said here (the ssllabs.com test):
http://kmeleonbrowser.org/forum/read.php?1,141148,141413,page=2#msg-141316
K-meleon is safe.
K-meleon 75.x could be not as safe, but K-meleon 76 (Gecko 38, has already the fix) so you don't need to worry, because that versions has all fixes needed.
Said that, doesn't mean that the stable 75.1 is insecure. Have in mind that for those attacks to be effective there MUST be a MitM attack. Otherwise, they won't happen. Ok, better secure than nothing, but it is unlikely we are unsafe, if we follow security practices, type the url, not following a link, check certificates, enable OCSP certificate verify, etc.
Anyway, you are on Windows 8.1, so you don't have any restrictions on browsers versions, so, if you feel unsecure, just use the latest by Mozilla or even Google Chrome.