Item/attachment box: Prevent default label focus/blur behavior

Since ceb1dd7da3 added a tabindex on
#zotero-view-item, clicking anywhere outside a field in the pane will
blur the active field. That's an improvement, but it conflicted with our
custom label behavior - when an active field's label is clicked, we want
to blur it and keep it blurred, but the default behavior is to re-focus
it on mouseup.

Fix by preventing the default focus behavior on mousedown/click.

chrome/content/zotero/elements/attachmentBox.js

@@ -264,7 +264,11 @@
 				}
 			});
 
-			this.querySelectorAll(".meta-label").forEach(label => label.addEventListener("click", this._handleMetaLabelClick));
+			for (let label of this.querySelectorAll(".meta-label")) {
+				// Prevent default focus/blur behavior - we implement our own below
+				label.addEventListener("mousedown", event => event.preventDefault());
+				label.addEventListener("click", this._handleMetaLabelClick);
+			}
 		}
 
 		destroy() {
@@ -625,6 +629,8 @@
 		}
 
 		_handleMetaLabelClick = (event) => {
+			event.preventDefault();
+			
 			let labelWrapper = event.target.closest(".meta-label");
 			if (labelWrapper.nextSibling.contains(document.activeElement)) {
 				document.activeElement.blur();

chrome/content/zotero/elements/itemBox.js

@@ -854,7 +854,15 @@
 				if (!this.editable) {
 					break;
 				}
-				label.addEventListener('click', (_) => {
+				
+				label.addEventListener('mousedown', (event) => {
+					// Prevent default focus/blur behavior - we implement our own below
+					event.preventDefault();
+				});
+				
+				label.addEventListener('click', (event) => {
+					event.preventDefault();
+					
 					let labelWrapper = label.closest(".meta-label");
 					if (labelWrapper.nextSibling.contains(document.activeElement)) {
 						document.activeElement.blur();