Is that a Addon or separate software?

It is not an addon nor separate software. It is a website and in this case I am using it to set up google map API's that I can use on my own websites.

What does the error screenshot say minus/blackout private info?

You could test with CSP disabled (globally) to confirm that is the source of the problem and not a side issue:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste csp and pause while the list is filtered

(3) Double-click the security.csp.enable preference to switch the value from true to false

I don't know whether that will take effect on the next reload of the page, or whether you need to restart Firefox before it takes effect.

Thanks, I did that (disabled csp) and no longer receive the csp error I showed earlier. However the page still does not work. I tried messing with privacy and cookie settings again after disabling csp to see if that made a difference, and it didn't. The first error I get now from Firefox's web console is the following:

ERROR Object { url: "https://cloudusersettings-pa.clients6.google.com/v1alpha1/settings/CONSOLE_PINS/keys/CLOUD?key=[removed]", headers: Map(6), status: 404, statusText: "Not Found", method: "GET", body: {…}, bodyText: "{\"error\":{\"code\":404,\"message\":\"Requested entity was not found.\",\"status\":\"NOT_FOUND\"}}", errorExperience: 1, trackingId: "c722062798", message: "Requested entity was not found.", … }

Again, there is no issue whatsoever accessing this Google platform console website with Chrome. I also used to be able to access this without error using Firefox but it has been about 6 months since I have needed to access it. So, something must have changed relating to this issue in Firefox's updates since the last time I used the Google platform console.

Thank you for the help!

A 404 Not Found seems like a response that wouldn't vary between browsers. If you compare the Network sections of the developer tools in Chrome and Firefox, do you see any difference between the requests?

Do you want to try:

New Profile Test

This takes about 3 minutes, plus the time to test your problem site(s).

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

Click the Create a New Profile button, then click Next. Assign a name like March2019, ignore the option to relocate the profile folder, and click the Finish button.

After creating the profile, scroll down to it and click the Set as default profile button below that profile, then scroll back up and click the Restart normally button. (There are some other buttons, but please ignore them.)

Firefox should exit and then start up using the new profile, which will just look brand new. Please ignore any tabs enticing you to connect to a Sync account or to activate extensions found on your system so we can get a clean test.

Do your problem site(s) work any better in the new profile?

When you are done with the experiment, open the about:profiles page again, click the Set as default profile button for your normal profile, then click the Restart normally button to get back to it.

Creating a new profile and logging into the Google console from that profile fixed the issue. So I tried replicating my original profile (adding add-in's/extensions/themes etc) to see if the issue would crop up again, and it didn't. Then, I copied the url of the Google console from the new profile, loaded the old profile and pasted in the url, and got no errors.

So it appears something in the url was causing the issue for whatever reason. Strange because I had logged out and logged in on Google several times in an attempt to solve the issue, but I think the errant url must have followed with the logout and login process, unnoticed by me.

Bottom line, the issue seems resolved at this point. Thank you so much for the tips; the creation of a new profile led me to discovering the real issue.