added "old browser" warning

index.html

@@ -661,9 +661,38 @@
                 elem.innerHTML = innerHTML
             return elem
         }
-
+        // detect browser version
+        function detectBrowser() {
+            let ua = navigator.userAgent,
+                tem,
+                M = ua.match(/(opera|chrome|safari|firefox|msie|trident(?=\/))\/?\s*(\d+)/i) || [];
+            if (/trident/i.test(M[1])) {
+                tem = /\brv[ :]+(\d+)/g.exec(ua) || [];
+                return 'IE ' + (tem[1] || '');
+            }
+            if (M[1] === 'Chrome') {
+                tem = ua.match(/\b(OPR|Edge)\/(\d+)/);
+                if (tem != null) return tem.slice(1).join(' ').replace('OPR', 'Opera');
+            }
+            M = M[2] ? [M[1], M[2]] : [navigator.appName, navigator.appVersion, '-?'];
+            if ((tem = ua.match(/version\/(\d+)/i)) != null) M.splice(1, 1, tem[1]);
+            return M.join(' ');
+        }
         window.addEventListener('hashchange', e => showPage(window.location.hash))
         window.addEventListener("load", () => {
+            const [browserName, browserVersion] = detectBrowser().split(' ');
+            const supportedVersions = {
+                Chrome: 85,
+                Firefox: 75,
+                Safari: 13,
+            }
+            if (browserName in supportedVersions) {
+                if (parseInt(browserVersion) < supportedVersions[browserName]) {
+                    notify(`${browserName} ${browserVersion} is not fully supported, some features may not work properly. Please update to ${supportedVersions[browserName]} or higher.`, 'error')
+                }
+            } else {
+                notify('Browser is not fully compatible, some features may not work. for best experience please use Chrome, Edge, Firefox or Safari', 'error')
+            }
             document.body.classList.remove('hidden')
             document.querySelectorAll('sm-input[data-btc-address]').forEach(input => input.customValidation = btc_api.validateAddress)
             document.addEventListener('keyup', (e) => {