firefox: fix wrapper autoconfig semicolon

The wrapper has a conditional checking for optional nix extensions. If
it exists it adds a preference line to the autoConfig file.

In the previous commit d3a6a12 the
conditional was added to the line in the config, but it missed the
semicolon at the end of the string. Leading to the autoConfig file
always having a seemingly random ; regardless of the condition.

Author: bentenjamin

pkgs/applications/networking/browsers/firefox/wrapper.nix

@@ -147,7 +147,7 @@ let
         // to be able to install addons that do not have an extid
         // Security is maintained because only user whitelisted addons
         // with a checksum can be installed
-        ${ lib.optionalString usesNixExtensions ''lockPref("xpinstall.signatures.required", false)'' };
+        ${ lib.optionalString usesNixExtensions ''lockPref("xpinstall.signatures.required", false);'' }
       '';
 
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