Roundcube provides a legacy plugin. Obviously they have the intention to support legacy browsers.
They're just a few people though, so if people want to support the legacy efforts, just contribute to the legacy plugin and help fix any bugs that exist.
https://github.com/roundcube/roundcubemail/tree/master/plugins/legacy_browse... https://github.com/roundcube/roundcubemail/tree/master/plugins/legacy_browser
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