When you are visiting the official Mozilla Add-ons repository, you may have noticed that some, or even most, of the extensions listed there are not as readable as others. Mozilla some time ago made a change to the add-ons pages that changed the style of incompatible add-ons. While that may sound like a good idea at first, you may come to the conclusion that it is not that great after all.
The major reason for this is that add-on compatibility can be forced in the browser. It is rare to find a recent add-on that is at its core not compatible with newer versions of the browser. If you are running beta, aurora or nightly builds of the browser, then you will see a lot of semi-transparent add-on listings on the Mozilla site.
The biggest issue usability-wise is that the add-on information become barely readable in the listings, but see for yourself.
You can click through to access the add-ons profile page which is displayed normally, but if you have lots of hard to read extensions listed on a page, you would spend lots of time doing so. Or, if you are eagle-eyed or do not mind concentrating on the listings, you could learn to live with it.
I on the other hand do not like the different opacity levels on Mozilla Add-ons at all, and would like to share two options to disable them,
NoScript - If you use NoScript you are good to go. Simply do not allow Mozilla.org to run scripts - which NoScript does automatically, to block the page from styling incompatible add-on listings differently. This works nicely and does not really interfere with add-on downloading and installing functionality.
If you do not use NoScript usually, it may feel like overkill to install the extension just to make incompatible add-ons readable again on the Firefox add-ons pages.
This Stylish script does the same thing. While you still need to install an add-on for the functionality, it is not something that is impacting your whole browsing experience like NoScript does. Simply install Stylish first, and once you have restarted the Firefox browser the userstyle to do away with different styles on the Mozilla Add-ons repository.