Bug 1356149 - Stop using flex for request list content; r=rickychien

MozReview-Commit-ID: KC1dg6cB4St

--HG--
extra : rebase_source : 90f8a08199d998776994d236f01522bc4c3682fb

devtools/client/netmonitor/src/assets/styles/netmonitor.css

@@ -186,11 +186,9 @@ body,
 }
 
 .requests-list-contents {
-  display: flex;
-  flex-direction: column;
+  height: 100%;
   overflow-x: hidden;
   overflow-y: auto;
-  flex: 1;
   --timings-scale: 1;
   --timings-rev-scale: 1;
 }