Comment 2 for bug 1573408

I was able to install the plug-in using the command line like this:

sudo dpkg -i google-talkplugin_current_amd64.deb

That produced this:

Selecting previously unselected package google-talkplugin.
(Reading database ... 196768 files and directories currently installed.)
Preparing to unpack google-talkplugin_current_amd64.deb ...
Unpacking google-talkplugin (5.41.0.0-1) ...
Setting up google-talkplugin (5.41.0.0-1) ...

After this, I restarted Firefox. I went to Gmail to make a phone call, and after clicking the "Allow" button prompted at the top of Firefox (under the address bar), it worked.

However, in previous versions of Ubuntu, I was able to install this with the GUI exclusively.