Tor Browser should run without a `/proc` filesystem.

Currently Tor Browser crashes immediately on startup if a proc filesystem is not mounted on /proc. This also affects the upstream firefox code, so it technically is a Mozilla bug.

too much recursion
Segmentation fault (core dumped)

/proc contains a large amount of information about the host system that can be used to fingerprint/identify users and additionally historically has been the source or part of many kernel security problems.

While this problem can be mitigated by a MAC system (eg: AppArmor) to constrain what Firefox can access under /proc, the ideal fix is for Firefox to support running without /proc, while degrading gracefully (there is no truly ubiquitous MAC system available on all common Linux distributions by default, and the problem is severe enough that it should be resolved correctly).