Use keywords for access key

From this version, access key would prefer keywords of search engine. You may noticed that access key is changed after upgrade to this version. This is intend behavior. You may config keyword in firefox configuration page. This changing is aimed to handle search engines whose name does not contain latin characters, such as baidu or yandex.

Add support for menu access keys

First stable release since Firefox 63 reached beta channel which means APIs this extension relay on should be stable.

fix failed to show search engines without favicon configured

Support new serach.search api

add "search" permission