Two things that may have happened. 1. That extension may rely upon an API that was removed from Firefox 40. Add-on developers were notified 9 to 10 months ago about one API that was deprecated and would replaced with a new similar API. That change 'broke' a number of extensions in Firefox 40. 2. Based upon the latest review for that extension - by Crystal on September 7, 2014 - that extension is 'dead' if it needs to be modified to continue to work. With the new "signing" feature for extensions, any opening and editing of the internal files for an extension will break the "signature" for the extension. Should still work in Firefox 40 - with an alert in the Add-ons Manager, but with Firefox 41 and later the 'signature' needs to be "verifiable". An override will be available in 41, but 42 and later with no signature or a broken signature - the extension won't install and if already installed it will be disabled, with no user recourse.

https://addons.mozilla.org/en-US/firefox/user/alexischr/ Only 33 users and not having been updated since June 19, 2013, along with no developer contact info doesn't look good for that add-on being usable now or in the future.

Is there a similar add on or program that can block blacklisted sites for 30-60 seconds after opening them?

Or a way to update this one to work with the new version of firefox?

Or is there a way to use an older version of firefox so this one will continue working?

I just loaded this extension from the Add-ons site and tried to go to Facebook and immediately got the black screen. It's annoying that if I switch to another window to get something done, when I return, the timer starts again. I'm not interested in looking at a black screen!

Have you tried removing and reinstalling the extension in case it is corrupted?

Separate Issue; Your System Details shows;

Installed Plug-ins

Shockwave Flash 11.9 r900 Shockwave Flash 18.0 r0
Having more than one version of a program may cause issues. You must remove the older programs. Then get the current full installer.

Note: Edge on Win10 does not use ActiveX version but its own Flash.

Flash: Grab the uninstaller from here: Uninstall Flash Player | Windows Uninstall Flash Player | Mac

Then reinstall the latest version.

Flash Player Version 18.0.0.232
https://www.adobe.com/products/flashplayer/distribution3.html Note: Windows users must download the “Internet Explorer” and “Plugin-based browsers” installers.

jscher2000 said

I just loaded this extension from the Add-ons site and tried to go to Facebook and immediately got the black screen. It's annoying that if I switch to another window to get something done, when I return, the timer starts again. I'm not interested in looking at a black screen! Have you tried removing and reinstalling the extension in case it is corrupted?

Ah that worked.

Apparently I accidentally messed up the coding a bit when trying to add a new website. Reinstalling it fixed it, and then it was just a matter of figuring out what I was coding wrong when trying to change the blacklist.

The lesson here is never to code on notepad.