The installation consists of two main steps: Copying the Markerbox files into Adobe's extension folder and telling your Adobe software to allow extensions to run that were not installed by Adobe.
In case you are installing a new version of Markerbox on the same version of Premiere / CSXS you can skip step 2.
1) Adobe Extension Folder
In the ZIP file you downloaded you will find a folder called "markerbox" with all necessary files included (approx. 450 kB). Copy or move this Markerbox folder into the Adobe extension folder. Before you do this make sure you have administrator rights and that you can see system folders and hidden folders.
On Windows, using the Windows Explorer, go to C:\Program Files (x86)\Common Files\Adobe\CEP\extensions
On macOS, using the Finder, go to /Library/Application Support/Adobe/CEP/extensions
In case these folders don't exist simply create them manually. When you copy the Markerbox folder into the extension folder you may need to confirm this action as an administrator.
Now Adobe Premiere Pro has everything to run the extension, apart from one thing ...
2) Trusting the Extension
Open your Registry Editor. You will find it by typing "regedit" in the search, at the bottom left corner. Go to the following folder: \HKEY_CURRENT_USER\SOFTWARE\Adobe
In this folder you will find one or more folders called CSXS followed by a number. Perform the following task in each of these folders:
By right-clicking in the right area create a new string value with the value name "PlayerDebugMode" and the value data "1" (without quotes). This will allow you to run extension without official signatures (developer mode).
In your terminal write "defaults write com.adobe.CSXS.10 PlayerDebugMode 1" (without quotes).
In case you are running more than one version of CSXS repeat this step for every version.
Now Adobe's programs will run extension without official signatures (developer mode).
On Windows and macOS:
Restart Adobe Premiere Pro. In your menu, under Windows > Extensions, you should now find Markerbox. If not try restarting your computer before taking any further steps. Normally this does it, and you are good to go.
In case Markerbox still doesn't appear in your extensions you might be running an older version of Adobe Premiere Pro. Markerbox requires at least Premiere Pro 13. If you have an older version you won't be able to use Markerbox. Sorry.
Why is there no installer?
Markerbox is a personal non-profit project, and my time is limited. Developing installers for Windows and macOS is very time consuming, and they can be an additional source of problems.
Therefore I prefer spending my time on adding new features to Markerbox. The installation procedure described above normally takes only a few minutes ... a lot less than it would take me to program a more comfortable solution.