For some reason the setting to wraps lines of text is really hidden away–
Edit > Preferences > Advanced > General > Config Editor
–then search for 'wrap'.
You can create custom categories for tasks (and events I assume), but they won't actually be registered and added to the dropdown list unless you add them via Settings > Calendar > Categories (at the bottom of that page). You can change the colour here too.
Thunderbird's great and all, but it's also messy!
A couple of times I've gotten stuck in situations where it would start, but no windows would actually appear, and it would just keep hogging CPU in the background.
Running thunderbird -safe-mode has always worked to fix things for me. Once you're back in Thunderbird you can try re-enabling add-ons to help determine the problem. For me it's always bloody Lightning.
Other things you might like to try are deleting everything in ~/.cache/thunderbird, and making sure the .parentlock is deleted when TB quits.
NB: You can filter RSS feeds that same way you do email messages. Tools > Message Filters > Filters For: …