How did Javascript get disabled in the first place? Anyway, the option to disable Javascript from the Options menu was removed in Firefox 23. It's now in the "hidden" about:config internal site.

1. Go to about:config via your Address Bar (Ctrl + L)
2. Click the button saying you'll be careful
3. Search for javascript.enabled and if it is set to false (bold), set it to true by double clicking it
4. Restart Firefox

Its already true when I checked it

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You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.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 cookies only from websites that cause problems.

"Clear the Cache":

• Edit > Preferences > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Edit > Preferences > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

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

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Still showing the error. I have also tried Chrome and get the same thing. I have not changed anything, other than ran updates on Linux Mint.

Still showing the error.

What actually is the error you get?