Do not use FastRenderedViewLine on Firefox on Windows7

src/vs/editor/browser/viewParts/lines/viewLine.ts

@@ -24,7 +24,7 @@ const canUseFastRenderedViewLine = (function () {
 		return true;
 	}
 
-	if (platform.isLinux) {
+	if (platform.isLinux || browser.isFirefox) {
 		// On Linux, it appears that zooming affects char widths (in pixels), which is unexpected.
 		// --
 		// Even though we read character widths correctly, having read them at a specific zoom level
@@ -32,6 +32,8 @@ const canUseFastRenderedViewLine = (function () {
 		// --
 		// This could be improved if we ever figure out how to get an event when browsers zoom,
 		// but until then we have to stick with reading client rects.
+		// --
+		// The same has been observed with Firefox on Windows7
 		return false;
 	}