diff --git a/internal/graphics/framebuffer.go b/internal/graphics/framebuffer.go
index 7c56b6df2..16cfa04e0 100644
--- a/internal/graphics/framebuffer.go
+++ b/internal/graphics/framebuffer.go
@@ -58,9 +58,13 @@ func newFramebufferFromTexture(texture *texture, width, height int) (*framebuffe
 const defaultViewportSize = 4096
 
 func (f *framebuffer) viewportSize() (int, int) {
-	if web.IsEdgeBrowser() {
+	// On some browsers, viewport size must be within the framebuffer size.
+	// e.g. Edge (#71), Chrome on GPD Pocket (#420)
+	if web.IsBrowser() {
 		return f.width, f.height
 	}
+
+	// If possible, always use the same viewport size to reduce draw calls.
 	return defaultViewportSize, defaultViewportSize
 }
 
diff --git a/internal/web/js.go b/internal/web/js.go
index 0e323f0fb..3ae242c57 100644
--- a/internal/web/js.go
+++ b/internal/web/js.go
@@ -22,6 +22,10 @@ import (
 	"github.com/gopherjs/gopherjs/js"
 )
 
+func IsBrowser() bool {
+	return true
+}
+
 func isIOS() bool {
 	ua := js.Global.Get("navigator").Get("userAgent").String()
 	if !strings.Contains(ua, "iPhone") {
@@ -44,8 +48,3 @@ func isAndroidChrome() bool {
 func IsMobileBrowser() bool {
 	return isIOS() || isAndroidChrome()
 }
-
-func IsEdgeBrowser() bool {
-	ua := js.Global.Get("navigator").Get("userAgent").String()
-	return strings.Contains(ua, "Edge")
-}
diff --git a/internal/web/notjs.go b/internal/web/notjs.go
index 3250b9ce0..bdd483258 100644
--- a/internal/web/notjs.go
+++ b/internal/web/notjs.go
@@ -16,10 +16,10 @@
 
 package web
 
-func IsMobileBrowser() bool {
+func IsBrowser() bool {
 	return false
 }
 
-func IsEdgeBrowser() bool {
+func IsMobileBrowser() bool {
 	return false
 }