Work around broken Alt keyup in Firefox

Firefox no longer sends keyup events properly for the Alt keys. Try
to sniff out the state of the Alt key by monitoring other events that
include its state.

1 files changed, 4 insertions, 0 deletions

diff --git a/core/util/browser.js b/core/util/browser.js
index ab0e7ee..7a78eee 100644
--- a/core/util/browser.js
+++ b/core/util/browser.js
@@ -56,6 +56,10 @@ export function isEdge() {
     return navigator && !!(/edge/i).exec(navigator.userAgent);
 }
 
+export function isFirefox() {
+    return navigator && !!(/firefox/i).exec(navigator.userAgent);
+}
+
 export function isWindows() {
     return navigator && !!(/win/i).exec(navigator.platform);
 }