A possible cause is security software (firewall) that blocks or restricts Firefox without informing you about that, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox.

See Server Not Found - Troubleshoot connection problems and Configure firewalls so that Firefox can access the Internet and http://kb.mozillazine.org/Firewalls

Don't seem to be a firewall issue as there is no any message or doesn't seem to be waiting for connection. The page just goes blank while transferring to secure channel or while opening a secure website. There is no message what so ever. Also didn't see such problem for my previous upgrades.

Another thing you can test:

1. Type about:config into the location bar and press enter
2. Accept the warning message that appears, you will be taken to a list of preferences
3. In the filter box type security.ssl.enable
4. Double-click on the preference security.ssl.enable_false_start to change its value to false
5. Re-start Firefox to see if you can connect to secure sites.

This problem may be related to Bug 591523 – Find a solution for TLS false start incompatible sites

The setting security.ssl.enable to false wasn't helpfull for me. Only i notice that with gmail https works, only not with https://addons.mozilla.org and perhaps others. Could it be something with the build in certificates?

It didn't work for me too ... I can't even open https://support.mozilla.com/en-US/questions/751415#answer-102126. It just goes blank.

I have/had the same issue. In my case the problem is related to going through a proxy server. I tested on another machine with and without the proxy and it breaks when going through the proxy.

I believe it is most likely an interaction between the proxy server and the feature described in the following blog post: http://blog.sidstamm.com/2010/08/http-strict-transport-security-has.h...

Interestingly enough, running under Private Browsing mode allows it to work through the proxy.

I didn't notice a config option to turn off the HTTP Strict Transport Security. Is it there and I just didn't notice it?

Two questions:

Can you tell us your proxy settings (if it's a public proxy we can test with)?

Can you try clearing your cookies and cache (Tools > Clear Private Data) and trying again through the proxy?

One more question: Can you tell me if there's anything in your Error Console (Tools > Error Console).

Sorry, after some investigation: this was a possibly bug caused by a bad Test Pilot study that was released (and has now been taken back). In order to fix it:

Go to about:config in your location bar and in the Filter box type: Custom Value

For all those prefs, right click and select reset.

You'll have to set up proxy settings again (talk to your system admin if you need help)

OR

Beta 5 seems to have a problem with a certain kind of proxy: NTLM. I don't think there's a workaround for beta 5 but there will be a fix in beta 6.

I have just reverted to FF 4 beta 4. I am behind a proxy beta 5 just doesn't work with https sites.

I can't find any values for those prefs in about:config. Is there any other work around to fix this problem?

I'm pretty sure it is related to the NTLM issue you mentioned, for me at least. I am behind a Microsoft Proxy server (internal company proxy).

Right, NTLM stands for NT LAN Manager (which is a Microsoft product)

My brief experiments seem to indicate that FF4b5 doesn't work for https sites with an authenticated (via NTLM) proxy, but does work for https sites via a non-authenticated proxy.

Internally https sites work fine with either type of proxy set.

Looking through the bug notes, it looks like there is a simple work around, switch to Private Browsing Mode.

Works for me for all https sites I have tested.

Yes, I think NTLM is the culprit in my case too. Does anyone know if this bug is fixed yet? If so, can download a nightly build (B6) to get around this problem?

Same here (behind an NTLM proxy at work). I've just tried using the Firefox profile manager to create a completely new profile, then re-entered my proxy settings. I thought this might simulate part of what Private Browsing would do, but it's had no effect on https websites.

I'm not keen on using Private Browsing for everything, as I'd like to have my browsing history remembered. I may need to switch back to Beta 4 until a fix is available, if I can figure out where to re-download it from.

Last I looked, the bug was supposed be fixed in the nightly builds, shortly after it was noticed. Notes about that are listed in the bug report:https://bugzilla.mozilla.org/show_bug.cgi?id=592197

It also looks like beta 6 might not be that far out, if you read the comments on that report.

izogi Beta 4 can be found here: http://releases.mozilla.org/pub/mozil.../4.0b4/. Just select the OS and version you need.

That's what I did for now on my work machine while I await beta 6. I had noted the Private Browsing mode above also and decided I didn't want to work that way either.

i have the same issue. after upgrading to beta5 unable to access any https sites.

i found a work arround for now.

Try to access https sites from Private Browsing. this works.