I agree with the previous reviewer that the new permissions look fishy, but it seems they are not currently abused. I unzipped the add-on and looked at the source.

"Exchange messages with programs other than Firefox" is used to communicate with the UI Vision XModule used for desktop OCR.

"Display notifications to you" is used to display notifications when you have a paid subscription that is about to expire, and for displaying messages when using the desktop capture feature.

"Access browser activity during navigation" I'm not sure about, it might be needed for some functionality to work but I didn't find anything obvious. There seems to be no feature like collecting browsing activity or something abusive like that.

Of course the permissions coul be used for abusive purposes in the future so it is always best to be a bit paranoid. Even with the permission system in Firefox you have to trust the developer to an extent.