I often get large pauses when TB is syncing up multiple mail accounts and can’t do anything while that is in progress.
Shouldn’t i be able to write and read mails on account a while account b is downloading massiv amounts of data?
Also i am a little allergic to the amount of JS being used in TB.
Wouldn’t the wise choice be to rewrite components in Rust, which is a programming language that is safer by design instead of javascript?
Ideally, yes. In practice, parts of the product are single thread that are not changing near term, complicated by the fact that there are factors both internal and external that can magnify performance issues. See Thunderbird:Testing:Memory Usage Problems - MozillaWiki
Some of the parts shared with Firefox are changing to Rust. AFAIK there is no Thunderbird-specific code moving to Rust, and in fact more TB code is moving to js as a necessary change to gradually become more web-friendy.
web-friendly = works in a browser or can run on browser technology. that is the general direction. whether it will be fully realized is yet to be determined.