Firefox ESR: uniformize locales' URLs

Use direct Mozilla CDN URL for all locales of Firefox ESR, like the main en-US
already does. Note that this is the official download location as
linked on
[mozilla.org](https://www.mozilla.org/en-US/firefox/organizations/all/),
with unchanged SHAs.

Casks/firefox-esr-ru.rb

@@ -2,7 +2,7 @@ cask 'firefox-esr-ru' do
   version '38.6.1'
   sha256 '5ad748abed1c78923988222ca5bb69730123d4756e8ae128e15b5ad4e39db4fe'
 
-  url "https://download.mozilla.org/?product=firefox-#{version}esr-SSL&os=osx&lang=ru"
+  url "https://download-installer.cdn.mozilla.net/pub/firefox/releases/#{version}esr/mac/ru/Firefox%20#{version}esr.dmg"
   name 'Mozilla Firefox'
   homepage 'https://www.mozilla.org/ru/firefox/organizations/'
   license :mpl

Casks/firefox-esr-uk.rb

@@ -2,7 +2,7 @@ cask 'firefox-esr-uk' do
   version '38.6.1'
   sha256 '173982d204a2db1a383d8e64ab6c0f074a97ffe318085dfbccd13f701a154838'
 
-  url "https://download.mozilla.org/?product=firefox-#{version}esr-SSL&os=osx&lang=uk"
+  url "https://download-installer.cdn.mozilla.net/pub/firefox/releases/#{version}esr/mac/uk/Firefox%20#{version}esr.dmg"
   name 'Mozilla Firefox'
   homepage 'https://www.mozilla.org/uk/firefox/organizations/'
   license :mpl

Casks/firefox-esr-zh-cn.rb

@@ -2,7 +2,7 @@ cask 'firefox-esr-zh-cn' do
   version '38.6.1'
   sha256 '21b4627fa774199453f22ef3877b7cd2926850ed8cdfb8a19498674c7eb45483'
 
-  url "https://download.mozilla.org/?product=firefox-#{version}esr-SSL&os=osx&lang=zh-CN"
+  url "https://download-installer.cdn.mozilla.net/pub/firefox/releases/#{version}esr/mac/zh-CN/Firefox%20#{version}esr.dmg"
   name 'Mozilla Firefox'
   homepage 'https://www.mozilla.org/zh-CN/firefox/organizations/'
   license :mpl