Replace browser conditions by preprocessed conditions

The extension used to rely on the isFirefox method to check whether the
browser is Firefox or Chromium-based. This CL removes this function and
replaces the conditions based in this function by conditions which are
pre-processed at compile time.

Change-Id: Id7280e6c8fb3dfd3fabbc05339ef3791822aa6ac
diff --git a/src/common/optionsPrototype.json5 b/src/common/optionsPrototype.json5
index 38cfaca..824b754 100644
--- a/src/common/optionsPrototype.json5
+++ b/src/common/optionsPrototype.json5
@@ -75,11 +75,13 @@
     context: 'options',
     killSwitchType: 'option',
   },
+  // #!if ['chromium', 'chromium_mv3'].includes(browser_target)
   'ccdragndropfix': {
     defaultValue: false,
     context: 'options',
     killSwitchType: 'option',
   },
+  // #!endif
   'batchlock': {
     defaultValue: false,
     context: 'options',