diff --git a/app/assets/stylesheets/pages/repo.scss b/app/assets/stylesheets/pages/repo.scss
index 00457717f00..7637a3f577c 100644
--- a/app/assets/stylesheets/pages/repo.scss
+++ b/app/assets/stylesheets/pages/repo.scss
@@ -306,8 +306,18 @@
 }
 
 .preview-container {
-  height: 100%;
-  overflow: auto;
+  flex-grow: 1;
+  position: relative;
+
+  .md-previewer {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    overflow: auto;
+    padding: $gl-padding;
+  }
 
   .file-container {
     background-color: $gray-darker;
@@ -347,10 +357,6 @@
       color: $diff-image-info-color;
     }
   }
-
-  .md-previewer {
-    padding: $gl-padding;
-  }
 }
 
 .ide-mode-tabs {
diff --git a/changelogs/unreleased/45934-ide-firefox-scroll-md-preview.yml b/changelogs/unreleased/45934-ide-firefox-scroll-md-preview.yml
new file mode 100644
index 00000000000..b9e70bc5679
--- /dev/null
+++ b/changelogs/unreleased/45934-ide-firefox-scroll-md-preview.yml
@@ -0,0 +1,5 @@
+---
+title: Fix unscrollable Markdown preview of WebIDE on Firefox
+merge_request:
+author:
+type: fixed