Update:
Mozilla Thunderbird, Portable Edition 31.7.0
After installation and open the software, it display that this is a daily build.
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It's an issue on Mozilla's servers. They released 31.7.0 and it's what you get if you go to the Thunderbird homepage and download it. But the internal servers aren't set to serve 31.7.0 updates and think 31.6.0 is current stable. So, since version is greater than what it thinks is stable, it shows as "daily". It'll go away as soon as Mozilla fixes their issue. The same thing happens on local installs and it happens for all languages.
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