Part 1 fix for bug #55899

themes/classic/communicator/directory/directory.css

@@ -76,3 +76,20 @@ treeitem[type="DIRECTORY"][loading="true"] > treerow > treecell > .tree-cell-twi
     font-style            : italic;
   }
 
+/**
+ * This fixes a bug. As you scroll down in a tree the computed column width
+ * can change. That would make the columns shift durning scrolling.
+ * So we give them inital preferred widths so they aren't computed.
+ */
+#FilenameColumn {
+  width: 100px;
+}
+
+#ContentLengthColumn {
+  width: 100px;
+}
+
+#LastModColumn {
+  width: 100px;
+}
+

themes/classic/global/mac/filepicker.css

@@ -17,3 +17,20 @@ treeitem.hidden > treerow > treecell > .tree-icon {
   list-style-image: url("chrome://global/skin/blank.gif");
 }
 */
+
+/**
+ * This fixes a bug. As you scroll down in a tree the computed column width
+ * can change. That would make the columns shift durning scrolling.
+ * So we give them inital preferred widths so they aren't computed.
+ */
+#FilenameColumn {
+  width: 100px;
+}
+
+#ContentLengthColumn {
+  width: 100px;
+}
+
+#LastModifiedDateColumn {
+  width: 100px;
+}

themes/classic/global/unix/filepicker.css

@@ -17,3 +17,21 @@ treeitem.hidden > treerow > treecell > .tree-icon {
   list-style-image: url("chrome://global/skin/blank.gif");
 }
 */
+
+/**
+ * This fixes a bug. As you scroll down in a tree the computed column width
+ * can change. That would make the columns shift durning scrolling.
+ * So we give them inital preferred widths so they aren't computed.
+ */
+#FilenameColumn {
+  width: 100px;
+}
+
+#ContentLengthColumn {
+  width: 100px;
+}
+
+#LastModifiedDateColumn {
+  width: 100px;
+}
+

themes/classic/global/win/filepicker.css

@@ -17,3 +17,21 @@ treeitem.hidden > treerow > treecell > .tree-icon {
   list-style-image: url("chrome://global/skin/blank.gif");
 }
 */
+
+/**
+ * This fixes a bug. As you scroll down in a tree the computed column width
+ * can change. That would make the columns shift durning scrolling.
+ * So we give them inital preferred widths so they aren't computed.
+ */
+#FilenameColumn {
+  width: 100px;
+}
+
+#ContentLengthColumn {
+  width: 100px;
+}
+
+#LastModifiedDateColumn {
+  width: 100px;
+}
+

themes/modern/communicator/directory/directory.css

@@ -76,3 +76,19 @@ treeitem[type="DIRECTORY"][loading="true"] > treerow > treecell > .tree-cell-twi
     font-style            : italic;
   }
 
+/**
+ * This fixes a bug. As you scroll down in a tree the computed column width
+ * can change. That would make the columns shift durning scrolling.
+ * So we give them inital preferred widths so they aren't computed.
+ */
+#FilenameColumn {
+  width: 100px;
+}
+
+#ContentLengthColumn {
+  width: 100px;
+}
+
+#LastModColumn {
+  width: 100px;
+}

themes/modern/global/filepicker.css

@@ -17,3 +17,20 @@ treeitem.hidden > treerow > treecell > .tree-icon {
   list-style-image: url("chrome://global/skin/blank.gif");
 }
 */
+
+/**
+ * This fixes a bug. As you scroll down in a tree the computed column width
+ * can change. That would make the columns shift durning scrolling.
+ * So we give them inital preferred widths so they aren't computed.
+ */
+#FilenameColumn {
+  width: 100px;
+}
+
+#ContentLengthColumn {
+  width: 100px;
+}
+
+#LastModifiedDateColumn {
+  width: 100px;
+}