SeaMonkey 2.53.5.1

What's new in this version:

- Uses the same backend as Firefox and contains the relevant Firefox 60.8 security fixes
- Shares most parts of the mail and news code with Thunderbird. Please read the Thunderbird 60.0 release notes for specific changes and security fixes in this release
- Additional important security fixes up to Current Firefox 78.4 ESR and a few enhancements have been backported. We will continue to enhance SeaMonkey security in subsequent 2.53.x beta and release versions as fast as we are able to.

Contains (among other changes) the following major changes relative to SeaMonkey 2.53.5:
- Fix advertising of av1 support bug 1490877
- Various security and general platform fixes

Contains (among other changes) the following major changes relative to SeaMonkey 2.49.5:
- The Bookmarks Manager has switched its name to Library, and now also includes the History list. When invoking History, the Library will be shown with the History list selected. The extensive modifications were needed because of Mozilla Gecko platform API changes.
- Download Manager has been migrated to a new API. Although it looks pretty much the same as before, the search option is missing and some other minor details work differently. The previous downloads history is removed during the upgrade.
- The layout panel was added to the CSS Grid tools
- TLS 1.3 is the default SSL version now
- The only NPAPI plugin which will work with SeaMonkey 2.53.5.1 is Flash. Support for other NPAPI plugins like Java and Silverlight has been removed. For displaying pdf files in the browser you can use pdf.js-seamonkey from Isaac Schemm.
- SeaMonkey now uses a new api for formatting regional data like time and date. Default is to use the application locale of the current SeaMonkey build. If you use a language pack or a different OS formatting this is usually not desired. You can change the formatting from the application locale to the regional settings locale (OS) in the preferences dialog under "Appearance".