My guess is the extension has been disabled due to recently discovered "
GLitch" rowhammer attack vector.
> EXT_DISJOINT_TIMER_QUERY is an OpenGL extension
developed to provide developers with more detailed
information about the performance of their applications [46].
This extension, if made available to the system by the GPU
driver, is accessible from both WebGL and WebGL2, and
provides the _javascript_ runtime with two timing sources:
(1) TIME_ELAPSED_EXT and (2) TIMESTAMP_EXT. Such
timers allow an attacker to measure the timing of secret
operations (e.g., memory accesses) performed either by the
CPU or the GPU.