The Firefox crash report published by Mozilla suggests that most of us cannot access Firefox's hardware acceleration.
The reason for this circumstance is simply outdated hardware and outdated drivers. Just because Firefox supports hardware acceleration does not mean that everyone will get it. A prerequisite for this feature is a driver from Nvidia and AMD that is at least from June 2010 or newer (Intel is a bit more complicated, but described in Mozilla's driver blacklist).
The bottom line is that currently only 30 percent of Windows Firefox users can access hardware acceleration and 49 percent can access WebGL. Predictably, the more recent the OS release, the greater likelihood of GPU support. For example, 67 percent of Windows 8 users can use Firefox hardware acceleration, versus 47 percent of Windows 7 users, 17 percent of Windows Vista users, and 13 percent of Windows XP users.
It may be somewhat surprising that just about 100 percent of Mac OS X users are supported, but then we have to remember that this feature arrived only in a Firefox version for Mac OS X 10.6 and higher – and naturally most machines that shipped with that OS have sufficient hardware to run hardware acceleration.
It's hard to say if these numbers apply to other browsers as well. Microsoft's only browsers with hardware acceleration are IE9 and IE10, which are supported from Windows Vista SP2 (IE9) and up (IE10 requires Windows 8). Chrome added the feature in Chrome 7 (developer version) and it is still incomplete today. Google does not release any data on how many people actually use this feature and what requirements Google may have. However, Mozilla's data is based on 300,000 to 800,000 monitored crashes today, which is rather substantial. This would at least suggest that most computer users today to do not have the necessary equipment to run browser hardware acceleration by Mozilla's standards.