iOS设备：
text-size-adjust: none !important;
-webkit-text-size-adjust: 100% !important;
-ms-text-size-adjust: 100% !important;
-moz-text-size-adjust: 100% !important;
安卓设备：

(function() {
        if (typeof WeixinJSBridge == "object" && typeof WeixinJSBridge.invoke == "function") {
            handleFontSize();
        } else {
            if (document.addEventListener) {
                document.addEventListener("WeixinJSBridgeReady", handleFontSize, false);
            } else if (document.attachEvent) {
                //IE浏览器，非W3C规范
                document.attachEvent("onWeixinJSBridgeReady", handleFontSize);
            }
        }

        function handleFontSize() {
            // 设置网页字体为默认大小
            WeixinJSBridge.invoke('setFontSizeCallback', {
                'fontSize': 0
            });
            // 重写设置网页字体大小的事件
            WeixinJSBridge.on('menu:setfont', function() {
                WeixinJSBridge.invoke('setFontSizeCallback', {
                    'fontSize': 0
                });
            });
        }
    })();