To try the thousands of add-ons available here, download Mozilla Firefox, a fast, free way to surf the Web!
CloseWelcome to Firefox Add-ons.
Choose from thousands of extra features and styles to make Firefox your own.
CloseReview for Dictionary Switcher by Jorg K
Rated 3 out of 5 stars
Sadly not compatible with Thunderbird 38 any more, since in that version the spell check language in the compose windows has been decoupled from the preference.
To create your own collections, you must have a Mozilla Add-ons account.