The spelling checker flags the proper noun "Thunderbird" as a misspelled word. Presumably we don't want to add every proper noun into the dictionary, but the name of the product seems like one it would be useful to add. I should note that over 31 million web pages contain the word "thunderbird" according to Google, and the first 100 results reference schools, an automobile model, a real estate agency, lodging of various kinds, a card game, a furniture manufacturer, and various other entities with the name in addition to the software, so it's certainly not uncommon.
That's odd, we added Thunderbird to the default en-US dictionary on the 1.8 branch for Thunderbird 2 along with Firefox, Mozilla, Google, eBay, SUSE, etc. Do those other words fail for you too Myk? Here's the full list of words we added to the dictionary: http://bonsai.mozilla.org/cvsview2.cgi?diff_mode=context&whitespace_mode=show&file=en-US.dic&branch=&root=/cvsroot&subdir=mozilla/extensions/spellcheck/locales/en-US/myspell&command=DIFF_FRAMESET&rev1=1.1&rev2=1.2 Can you double check that you are using the en-US dictionary as well?
Hmm, how bizarre. Now I can't reproduce the problem either, although I tested with both 1.5 and with the latest 2 nightly before filing the bug. But perhaps when I thought I was testing with 2 I was actually testing with 1.5 again.
ah that could be it. 1.5 would have flagged Thunderbird as being mispelled.