You are on the beta track. Let me discuss add-ons first:

As you've noticed, Firefox 41 requires that extensions be signed by Mozilla, which follows a brief review process. Presumably the publishers of many of your extensions that before Firefox 41 is officially released in about 5 weeks.

Would you want to run the current release, Firefox 40.0.2, instead of the beta test release? It doesn't block unsigned extensions. You can grab that here (scroll down to your preferred language): https://www.mozilla.org/firefox/all/

Alternately, you can flip a setting that exists only in Firefox 41 to allow unsigned extensions. That can be found here:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste xpi and pause while the list is filtered

(3) Double-click the xpinstall.signatures.required preference to switch it from true to false

Does one of those suggestions resolve the issue?

Could you describe the problem with private windows in more detail? For example:

• Can't open a new private window from the menu or using Ctrl+Shift+p
• Right-click, Open Link in New Private Window doesn't do anything
• Private windows open but do not load pages
• Something else

For the script issue notification, could you make a note of what it is the next time you see it, or grab a screen shot of it?

By the way, if you decide to switch to the release track, I suggest doing it this way:

Clean Reinstall

We use this name, but it's not about removing your settings, it's about making sure the program files are clean (no inconsistent, corrupted, or alien code files). As described below, this process does not disturb your existing settings. Do NOT uninstall Firefox, that's not needed.

(A) Download a fresh installer for Firefox 40.0.2 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

(B) Exit out of Firefox (if applicable).

(C) Rename the program folder, either:

(64-bit Windows folder names)

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\Fx41

(32-bit Windows folder names)

C:\Program Files\Mozilla Firefox

to

C:\Program Files\Fx41

(D) Run the installer you downloaded in (A). It should automatically connect to your existing settings.

Success?

Note: Some plugins may exist only in that Fx41 folder. If something essential is missing, look in these folders:

• \Fx41\Plugins
• \Fx41\browser\plugins

jscher2000 said

Could you describe the problem with private windows in more detail? For example:

• Can't open a new private window from the menu or using Ctrl+Shift+p
• Right-click, Open Link in New Private Window doesn't do anything
• Private windows open but do not load pages
• Something else

I got your message that "PW opens for a few seconds then closes."

That's strange, I can't think of what would cause that. Especially if normal new window are left unmolested.

Thanks, your email prompted me to look much closer at what is happening.

It is opening a duplicate FX without a tab for Private viewing with the other tabs. Same results no matter what instruction is used to request a private tab.

Does this help?

That's even stranger... Is it possible that the private window is minimized or hidden behind the main Firefox window?

If you have Firefox set to start up automatically in private mode, then it does behave differently from having a regular session and opening a private window. Seems you would notice the difference, but please check your setting here just in case:

"3-bar" menu button (or Tools menu) > Options > Privacy

If the selector says "Firefox will: Never remember history" then Firefox using automatic private browsing. You can change that to "Firefox will: Use custom settings for history" and uncheck the box for automatic private browsing to switch back.

OK, progress and resolution.

I was using Firefox will: Use custom settings for history but had the box checked. Unchecking it has solved the issue.

I am curious. Do the instructions on this page apply only to Private Window or generally across Firefox.

I realyy appreciate your efforts on my behalf. Sincere thanks. I rarely use Private but hate it when anyhting is unreliable.

The privacy settings apply to all windows. But private windows have a separate "cookie jar" which is shared between them and emptied when you close all the private windows.