Avast update broke Firefox

[LGM]

I updated the Avast program last night. Today I couldn't open Firefox. It wouldn't start at all. After some troubleshooting by starting Firefox in safe mode and disabling all add-ons, I was able to isolate the problem to the Avast Online Security 9.0.2018.95 add-on. When just that add-on is disabled, Firefox starts normally. When enabled, Firefox refuses to even start.

Is there some setting or tweak that needs to be made to enable this add-on to work in Firefox?  Alternately, how do I rollback to the previous version of Avast, including the add-on?

Please note I am running a very old version of Firefox on purpose so as to still make use of an invaluable add-on that does not work with newer Firefox versions. 

[Para-Noid]

You can safely disable or uninstall the "avast online security".
The real protection is provided by the web shield.

To uninstall the AOS...Control Panel>Uninstall a Program>double click "avast">click "change">untick the "browser protection">reboot

[LGM]

Sometimes, when I am browsing,  Avast will prevent Firefox from landing on a certain web page and it will send up a warning message about that web page being possibly infected. I want to keep that capability.

Are you sure "online security" is not responsible for that?

[Para-Noid]

Without seeing the pop-up I will venture a guess it's the web shield that is making the pop-up.
IOW it's the web shield that is protecting you. You may safely either disable the AOS or uninstall
it as directed above. The AOS is called "browser protection" in the list. The web shield is doing
the actual protection.

[LGM]

Paranoid -- the popup or message is just a small area in the lower right corner of the screen to let you know Avast has blocked a visit to a potentially harmful web page.

I get this message/block maybe once a month or once every two months and I want to keep this capability.

Thanks for your help. For now I will keep the "Online Security" add-on installed but disabled.

[Para-Noid]

The pop-up is probably the web shield and has nothing to do with the AOS extension.
To bring it back up...right click on the avast tray icon>click "show last pop-up".
If possible could you provide a screenshot? 
The AOS extension is mostly to prevent tracking.

[Ninjagranny]

Aos is killing firefox currently - as above just disable it .

Also meant to say that it is having problems with IMAP on Thunderbird as well. But stuff happens avast are great at finding and fixing problems it will all work again soon .

[LGM]

The pop-up is probably the web shield and has nothing to do with the AOS extension.
To bring it back up...right click on the avast tray icon>click "show last pop-up".
If possible could you provide a screenshot? 
The AOS extension is mostly to prevent tracking.

"Show last pop-up" is grayed out right now. And, at any rate, I don't recall the last time I got that pop-up about a blocked page; could have been weeks ago. So it wouldn't show now anyway.

If you direct me to a page that might trigger the popup but is otherwise safe, I will capture the screenshot for you.

[Para-Noid]

If you direct me to a page that might trigger the popup but is otherwise safe, I will capture the screenshot for you.

That is something I won't do. The reason for my refusal is the potential for you to get an infection.
If by chance it happens again take a good look and the pop-up itself will tell what triggered the pop-up.

[LGM]

OK, thanks Para-Noid. Usually I don't pay much attention to those things, but I'll keep an eye out.