This update to SeaMonkey 2.53.15 brings the following changes:

* Microtasks and promises bug 1193394.
* Implement queueMicrotask()bug 1480236.
* Remove old synchronous contentPrefService from the tree bug 886907
and bug 1392929.
* Remove remaining uses of 'general.useragent.locale' bug 1410736
and bug 1410738.
* Migrate to intl.locale.requested.locale list from
'general.useragent.locale' bug 1441016.
* Introduce a pref to store BCP47 locale list bug 1414390, bug
1423532 and bug 1441026.
* Remove synchronous certificate verification APIs from
nsIX509CertDB bug 1453741 and bug 1453778.
* Taskbar preview's favicon appears blank bug 1475524.
* Call Imagelibs decodeImageAsyncWindows using a callback bug
1790695.
* Remove PermissionsService from process Windows sandboxing code bug
1788233, bug 1789782 and bug 1794394.
* Security info dialog doesn't show cert status anymore bug 1293378.
* Replace nsIPlatfromCharset in mailnews bug 1381762.
* Replace use of nsMsgI18NFileSystemCharset() with
NS_CopyUnicodeToNative/NS_CopyNativeToUnicode() bug 1506422.
* Cater for Outlook's/Hotmail's 'Deleted' folder bug 1320191.
* Make some filter methods scriptable bug 1497513.
* Fix crash in nsMsgFilterAfterTheFact::ApplyFilter() caused by
async reset of 'm_curFolder' bug 537017.
* Localize messages from nsIMsgFolder.logRuleHitFail() bug 1352731.
* Add logging of message filter runs and actions bug 697522.
* Check that we got a non-null header before running a filter on it
(and crashing) bug 1563959.