User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0
Thanks for all the responses. Interesting that fragments do not seem to
be an option out there.
However raising the dependencies from time to time to get rid of legacy
code seems to be the most pragmatic option.
I guess thats one reason why projects want to be part of the release