Firefox users aren’t liking the new add-ons manager developed on HTML in Firefox 68. when compared with old UI, the new design requires more clicks to do manual updates and reach Details, Release notes and Permissions.
Firefox subreddit thread with subject “Extremely poor add-ons manager UI design in 68” got 489 points at the time of writing with 95% upvoted. This shows users dislike towards the new UI, on the other hand, Mozilla responded to this and said based on that feedback, they’ll incorporate changes for add-ons manager in the upcoming releases.

Mozilla used HTML technology for about:config and about:addons pages. This is the rewrite of design from the beginning. The old UI provided “Disable”, “Remove” and “Options” controls directly for each extension whereas new UI hides them in the 3-dot menu.
The extension description, newly added Permissions, and Release notes are buried where users need to select “More options” in extension menu to access.

The new design is clumsy with Recommended Extensions and Recommended themes if you’ve more extensions installed, that’s not a pretty page to look at for sure.
We’ve definitely heard the feedback that things could be improved. Expect to see more clean up and refinement in upcoming releases as we incorporate feedback.
— caitmuenster 🧀 (@caitmuenster) July 10, 2019
If you don’t like new add-ons manager design, you can disable it by changing the below preference value to false in about:config
extensions.
that was quick, why don’t they bring back the add-on bar while they are at it
You can get back to old add-ons manager by toggling this pref extensions.htmlaboutaddons.enabled