Please explain the problem in detail. What happens? What are the exact error message(s) ?

Make sure you are not blocking content.

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

One issue that seems more common lately is Firefox's Content Blocking. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature:

https://support.mozilla.org/en-US/kb/content-blocking

On my hosted class site and select to Embed some code. A screen pops up & I paste the code I want in (that's previously worked), I click the Submit button .... and I immediately get the CAPTCHA screen. I identify the requested picture segments, it seems to accept the answer, but the code I added to the input screen is not there. And my Homepage is the school default from CR. Therefore I think either Firefox has something to do with blocking my upload OR the host of my website is blocking it. As stated, this html code worked before, & all of a sudden it doesn't.

Contact their support and ask questions.

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows the shield icon at the left end of the location/address bar in case Content Blocking is blocking content.

• click the shield icon for more details and possibly disable the protection

You can check the Web Console about what content is blocked

• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/content-blocking