Bug 1783882 - Don't flex searchbar listbox. r=dao

I can't reproduce this on Linux (which would make it easier to dig into what's
going on), but I confirmed this fixes the issue on Windows.

The flexing algorithm of XUL doesn't deal well with the footer block.

This shouldn't be needed, I think, because the listbox height is handled
explicitly in

  https://searchfox.org/mozilla-central/rev/6a37a2ab9328bec6a29f688d1b2fba6974d34905/toolkit/content/widgets/autocomplete-popup.js#361

Also use CSS rather than attributes to flex stuff.

Differential Revision: https://phabricator.services.mozilla.com/D154133

browser/components/search/content/autocomplete-popup.js

@@ -108,11 +108,11 @@
     static get markup() {
       return `
       <hbox class="search-panel-header search-panel-current-engine">
-        <image class="searchbar-engine-image"></image>
-        <label class="searchbar-engine-name" flex="1" crop="end" role="presentation"></label>
+        <image class="searchbar-engine-image"/>
+        <label class="searchbar-engine-name" flex="1" crop="end" role="presentation"/>
       </hbox>
       <menuseparator class="searchbar-separator"/>
-      <richlistbox class="autocomplete-richlistbox search-panel-tree" flex="1"></richlistbox>
+      <richlistbox class="autocomplete-richlistbox search-panel-tree"/>
       <menuseparator class="searchbar-separator"/>
       <hbox class="search-one-offs" is_searchbar="true"/>
     `;

browser/themes/shared/searchbar.css

@@ -113,6 +113,7 @@
 .search-panel-tree {
   background: transparent;
   color: inherit;
+  -moz-box-flex: 0;
 }
 
 .search-panel-tree > .autocomplete-richlistitem {

toolkit/content/widgets/autocomplete-popup.js

@@ -127,7 +127,7 @@
 
     static get markup() {
       return `
-      <richlistbox class="autocomplete-richlistbox" flex="1"/>
+      <richlistbox class="autocomplete-richlistbox"/>
     `;
     }
 

toolkit/content/xul.css

@@ -523,6 +523,7 @@ search-textbox {
 .autocomplete-richlistbox {
   -moz-user-focus: ignore;
   overflow-x: hidden !important;
+  -moz-box-flex: 1;
 }
 
 .autocomplete-richlistitem {