Hi hadenp, JavaScript definitely is enabled by default.

Where are you getting this error:

It shows up as enabled but if I close/reopen Firefox, it gives me the not enabled error.

If this occurs on a page you restored from a previous session, Firefox might not have re-run all the bits and pieces necessary to get you back where you were. You could try reloading the page to straighten things out. Does Command+R or the Reload button on the toolbar help?

But if you mean the preference javascript.enabled flipped from true to false in about:config, check out the issues mentioned in the following article for some possible causes: How to fix preferences that won't save. (About:config? See: Configuration Editor for Firefox)

You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Options/Preferences).

"Remove the Cookies" for websites that cause problems:

• Options/Preferences -> Privacy & Security
  Cookies and Site Data: "Manage Data"

"Clear the Cache":

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Clear Data -> Cached Web Content: Clear

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems