Firefox incompatibility?

[algebravictor]

I just tried to register on projecteuler.net using firefox (the latest version) on a mac. The registration kept getting rejected saying that I had entered an incorrect confirmation code (Captcha). I found that it worked properly when using Safari. Now I get the same error when trying to log in using firefox, but not Safari. Clearly you a bug. Can this be fixed?

[euler]

I use Firefox myself.

Our website uses very strict security headers and the problem is probably due to a broken add-on. The most likely culprit will be a dodgy version of adblock. Again, I use an adblock myself. But there are lots of versions of adblock and they are not created equal. Try disabling it to see if it makes a difference. If it does, remove it immediately because it is doing something very naughty in the background without your knowledge.

If it's not an adblock, maybe it's another plugin.

Sometimes being in developer mode (with certain settings enabled) can cause the problem.

If you identify the culprit, please let me know because it's good to be aware of the cause.

[algebravictor]

Thanks. I think that I found the culprit. It's the following extension: iCloud Passwords. This allows firefox to retrieive passwords from the Apple iCloud (which I find useful). When I disabled it, things worked.

[euler]

That's great to hear it's working for you again, but I'm really surprised it's that extension.

If anyone reading this might have any ideas as to why our security headers are clashing with this extension, and ultimately interfering with sessions, I'd love to know. Especially if there is a fix we can implement that doesn't compromise our own security.