URL of affected sites
First of all, and although possibly not related to your problem, I will remind you that the version of Firefox you are using at the moment as been discontinued and is no longer supported. Furthermore, it has known bugs and security problems. I urge you to update to the latest version of Firefox, for maximum stability, performance, security and usability. You can get it for free, as always, at getfirefox.com.
As for your issue, you may be having a problem with some extension or plugin that is hindering your Firefox's normal behavior. Have you tried disabling all add-ons (just to check), to see if Firefox goes back to normal?