diff --git a/toolkit/themes/linux/global/search-textbox.css b/toolkit/themes/linux/global/search-textbox.css
index 2a3f55d93bdc..ae697454684f 100644
--- a/toolkit/themes/linux/global/search-textbox.css
+++ b/toolkit/themes/linux/global/search-textbox.css
@@ -28,6 +28,7 @@ html|input {
   text-shadow: inherit;
   box-sizing: border-box;
   -moz-box-flex: 1;
+  min-width: 0;
   text-align: inherit;
 }
 
diff --git a/toolkit/themes/osx/global/search-textbox.css b/toolkit/themes/osx/global/search-textbox.css
index 50c8e9464981..a75c9a386dc2 100644
--- a/toolkit/themes/osx/global/search-textbox.css
+++ b/toolkit/themes/osx/global/search-textbox.css
@@ -26,6 +26,7 @@ html|input {
   text-shadow: inherit;
   box-sizing: border-box;
   -moz-box-flex: 1;
+  min-width: 0;
   text-align: inherit;
 }
 
diff --git a/toolkit/themes/shared/global-shared.css b/toolkit/themes/shared/global-shared.css
index 5eb30fa66810..af4cf4b6133a 100644
--- a/toolkit/themes/shared/global-shared.css
+++ b/toolkit/themes/shared/global-shared.css
@@ -78,6 +78,11 @@
   padding: 0;
 }
 
+moz-input-box,
+html|input {
+  min-width: 0;
+}
+
 html|button,
 html|input,
 html|textarea {
diff --git a/toolkit/themes/windows/global/search-textbox.css b/toolkit/themes/windows/global/search-textbox.css
index bd2f7146f3da..b333a5f1a100 100644
--- a/toolkit/themes/windows/global/search-textbox.css
+++ b/toolkit/themes/windows/global/search-textbox.css
@@ -28,6 +28,7 @@ html|input {
   text-shadow: inherit;
   box-sizing: border-box;
   -moz-box-flex: 1;
+  min-width: 0;
   text-align: inherit;
 }