I've had a few too. Part of it is extensions not having been updated to support 1.5 yet. It's not been anything too severe though.
True. It's been improving since it was updated though - it was terrible. Check to see if it's fully updated.
A bit alright. Close it when you're not using it and it doesn't seem to be a problem. Genuine problem though.
I haven't had any of those. For the last one, I'd suggest you just reinstall them (delete them in the folder C:\Program Files\Mozilla Firefox\searchplugins, then reinstall from
https://addons.mozilla.org/search-engines.php?application=firefox).
It happens. As they're updated, you'll see that go away. Short term, this extension can force compatability, though it's not exactly a garuantee!
http://users.blueprintit.co.uk/~dave/web/firefox/buildid/nightly.html