diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 74f1e2e1..228416ce 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -15,8 +15,8 @@ Here is a list of typical questions I asked to existing reports:
 
  * **Does the problem appear with the [latest develpment build](http://piro.sakura.ne.jp/xul/xpi/nightly/)?**
    Possibly, problems you met has been resolved already.
-   On Firefox 43 and later you need to set `xpinstall.signatures.required` to `false` via `about:config`, to try such unsigned packages of development builds.
-   For Firefox 46 and later, you'll have to try an unbranded Firefox (including Beta, Aurora, and Nightly) to try development builds because the option will be removed on official Firefox 46 and later.
+   On Firefox 43 and later you need to set , to try such unsigned packages of development builds.
+   For Firefox 48 and later, you'll have to use an [unbranded Firefox](https://wiki.mozilla.org/Add-ons/Extension_Signing#Unbranded_Builds) (including Beta, Aurora, and Nightly) with a secret preference `xpinstall.signatures.required`=`false` (you can set it via `about:config`), to try unsigned development builds.
  * **Does the problem appear without Tab Mix Plus or something other tab related addon?**
    If a compatibility issue with other addons is reported without such information, it is very hard to be resolved.
    See also the next to next.