Merge pull request #9342 from simshaun/bug-9341

Fixes #9341 - Firefox flexbox input-group-field width

diff --cc scss/forms/_input-group.scss
index 33995a7c44f515905fa417217f48e124954a7e19,2fbfa9360363bef73a2b69bb5f5d3721336e97bc..887ff326719e8208ce2f110e8e2cb5087f53f32b
--- 1/scss/forms/_input-group.scss
--- 2/scss/forms/_input-group.scss
+++ b/scss/forms/_input-group.scss
@@@ -89,9 -88,11 +89,10 @@@ $input-prefix-padding: 1rem !default
      @extend %input-group-child;
      border-radius: 0;
  
 -    // scss-lint:disable ZeroUnit
      @if $global-flexbox {
 -      flex: 1 1 0px;
 +      flex: 1 1 0px; // sass-lint:disable-line zero-unit
        height: auto;
+       min-width: 0;
      }
      @else {
        height: $height;