It is my understanding that FreeBSD 5.3 is to comply with the static TLS mechanism specified by the ELF ABI
employed on Linux/Solaris. Until this or a comparable static TLS mechanism is made available, the only options yielding adequate performance (i.e. single instruction access to TLS data) are the TLS mechanism currently employed by the NVIDIA driver (in combination with linuxthreads
libc_r) or no TLS at all (i.e. a thread-unsafe driver). If your application requires a thread-safe OpenGL implementation, the latter obviously is no option at all.
There was a lengthy discussion leading up to the current developments on the FreeBSD threads
mailing list, in case you're interested in details.