Can't get to work with localhost
I am developing locally and attempting to use your extension while my site is running on localhost and all I get are blank windows. I have enabled the setting to use local files and that is good for pulling up /home/websites/testingSite/index.html however I am using Gatsby on this project, running a local server with http://localhost:8000 and I am unable to load it.
are there any errors in the console?

I have enlarged the console so you can see it. - No errors though.
So if I try to refresh the page I actually get something....

I am using Windows 10. Developing with Gatsby. I use VS code and Chrome Canary. Although I tried it on regular Chrome too and it would not work. Same results. -Sorry I did not put this in my original issue- I also tried this on Linux Mint and I am getting the same behavior using regular Chrome.
can you pull the source code and build the extension? there's a bunch of fixes on the networking side of the extension, meanwhile, I will check the extension on gatsby projects.
Ok... I cloned the repo => installed dependencies => ran npm build => I installed the build as an unpacked extension in Chrome on Windows 10 as well as Linux Mint. Still no luck. I really like the extension so I went a bit further...
I tried to look at it with gatsby develop as well as gatsby develop -H 0.0.0.0 -p 8000 with no luck on either.
However... The only good luck I can report, is that this looks like something with Gatsby. When I ran a Svelte/Sapper project in dev mode on localhost:3000 with the Sapper framework.. It worked perfect. It appears that this is specific to Gatsby.
I found a workaround..
The only way I can get content to render in the iframes and not just be blank, is after the initial load, go to the screen selection tab and deselect then re-select one of the screens. Does not matter which one. After that it triggers all the screens to re-render... then it loads on all of the screens still selected.
Still not sure why this is happening with Gatsby projects, but at least I am able to use the extension for now.
I am not sure if this will help you at all... but if anyone else is working with Gatsby and has this problem, at least it will work. Just a matter of hitting a button twice once it is loaded.
I can confirm that the workaround is working, however it's very annoying :(