Hi, I'd like to know what is this unusual version of Thunderbird. I was browsing the Thunderbird addons page when I searched for the phrase "test" and clicked the word "Any Thunderbird" under the "WORKS WITH" category. In the list of Thunderbird versions, the first one was Thunderbird 9999.0 . What version is this? I can't seem to find any info about it on Google. Could someone explain to me about why this version exists and why there isn't any information about it?

Thanks.