2699: spoof Navigator API

https://reviewboard.mozilla.org/r/147474/diff/4#index_header

I would have thought rounding DOWN to the nearest multiple of 10 would be better. Imagine being on FF61 and claiming to be 70 = might cause site issues

user.js

@@ -1452,6 +1452,9 @@ user_pref("privacy.firstparty.isolate.restrict_opener_access", true);
    [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1217238
  ** spoof/disable performance API (see 2410-deprecated, 2411, 2412) (FF56+)
    [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1369303
+ ** spoof Navigator API (see section 2697) (FF56+)
+    The version number will be rounded to the "nearest" multiple of 10
+    [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1333651
 ***/
 /* 2699a: enable privacy.resistFingerprinting (FF41+)
  * [1] https://bugzilla.mozilla.org/show_bug.cgi?id=418986 ***/