You could disable the built-in Inspector by setting the devtools.inspector.enabled to false on the about:config page (search devtools.*.enabled for more).

Firefox Shortcut keys

• https://developer.mozilla.org/en-US/docs/Tools/Keyboard_shortcuts

Read the question carefully. By the way. the shortcuts show that CTRL+SHIFT+C works for inspector, but it does not. I HAVE TESTED THIS IS IN SAFE-MODE TOO.

Hello,

Did you already try reset Firefox?

• Reset Firefox

In my computer I use Ctrl+Shift+I to open the Inspector. WIN8x64 Ctrl+Shift+C doesnt have function.

resetting firefox helped, but use it as a last option.

Note that such issues can be caused by your Firefox locale.
We have seen reports before that devtools entries are broken in a locale other than en-US.

Change the en-US to the language code of your locale:

• resource:///chrome/en-US/locale/browser/devtools/inspector.properties