How to See add-on version number like before in Firefox. Mozilla has stopped showing add-on version information in Add-ons manager in Firefox 41 (currently in Nightly). When you visit Add-ons page, you first see version numbers for add-ons, if you want Firefox to show that like before you can by using Classic Theme Restorer.
Make Firefox Add-ons Page to display Add-on Versi0n Information
1. Install Beta of Classic Theme Restorer (CTR) from AMO
2. Click on the Menu > Add-ons >Extensions, click on options for CTR, select ‘General UI (1)’, scroll down on the right side and select ‘Add-ons page: display add-on version’ (check the screenshot below).
3. Click ‘OK’.
Note: Without installing the extension and make the above mentioned change, you can still know version number of any add-on by clicking on the particular add-on or hover over it with mouse pointer to see in a tooltip.