Summary:
The Blue Ocean Pipeline Editor doesn't load at all in Microsoft Edge. But the same steps work perfectly with Google Chrome.

Steps to recreate:
1. In Blue Ocean, go to any Pipelinewhich is using a declarative Jenkinsfile as its basis:

2. Click on a branch with a successful build. In this case, I chose master:

3. Click the pencil icon. You'll be taken to a blank screen:

4. Now, using Google Chrome, repeat the exact same steps 1-3 as above. This time, you'll see the editor: