Revert mozilla store compliance changes

This reverts commit 97b6699afe.

Vencord is dropping support for the firefox extension, so these changes
are now obsolete. revert so users can still install the extension
manually and enjoy the full experience

src/utils/constants.ts

@@ -389,5 +389,3 @@ export const DevsById = /* #__PURE__*/ (() =>
             .map(([_, v]) => [v.id, v] as const)
     ))
 )() as Record<string, Dev>;
-
-export const IsFirefox = IS_EXTENSION && navigator.userAgent.toLowerCase().includes("firefox");