diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 228416ce..6f717341 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -15,8 +15,7 @@ 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 , 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.
+   On 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.