I don't think Firefox uses openGL. That is usually a gaming thing.
 
I would see if new video drivers are available, then try latency monitor and see if anything is stealing processing time.
http://www.resplendence.com/latencymon
 
Task Manager 'processes' would show if some service is running of which you are unaware.
 

Thanks for the link to the performance test, microapp. 
 
Here's the results so far -
 
Some meters in the far red, one is full scale - would post image but can't find link to upload images.  There was also a report - video card does come up in the report along with a ton of other stuff, even though i only have what i need in the windows start up feature.
 
So here's part of the report file from the test:
...
MEASURED INTERRUPT TO USER PROCESS LATENCIES
_________________________________________________________________________________________________________
The interrupt to process latency reflects the measured interval that a usermode process needed to respond to a hardware request from the moment the interrupt service routine started execution. This includes the scheduling and execution of a DPC routine, the signaling of an event and the waking up of a usermode thread from an idle wait state in response to that event.

Highest measured interrupt to process latency (µs):   3726.043589
Average measured interrupt to process latency (µs):   5.182842

Highest measured interrupt to DPC latency (µs):       119.154203
Average measured interrupt to DPC latency (µs):       0.723663
_________________________________________________________________________________________________________
 REPORTED ISRs
_________________________________________________________________________________________________________
Interrupt service routines are routines installed by the OS and device drivers that execute in response to a hardware interrupt signal.

Highest ISR routine execution time (µs):              538.128894
Driver with highest ISR routine execution time:       dxgkrnl.sys - DirectX Graphics Kernel, Microsoft Corporation

Highest reported total ISR routine time (%):          0.065223
Driver with highest ISR total time:                   hal.dll - Hardware Abstraction Layer DLL, Microsoft Corporation

Total time spent in ISRs (%)                          0.157338

ISR count (execution time <250 µs):                   396309
ISR count (execution time 250-500 µs):                0
ISR count (execution time 500-999 µs):                3
ISR count (execution time 1000-1999 µs):              0
ISR count (execution time 2000-3999 µs):              0
ISR count (execution time >=4000 µs):                 0
...
 
There is something called a 'Rapport Management System' on the list under 'processes' - this 'Rapport' thing is something that i uninstalled last year when i discovered it was responsible for giving Sonar constant hiccups.  It took ages to figure it out because a system restore would fix the hiccups, but only for a while, because 'rapport' would mysteriously reappear at some point without my knowing.  The first time it reappeared there it was, just sitting there in my tray smirking at me, threatening me with menace, invading my space, uninvited.  A chill ran down my spine - 'Is that 'rapport' icon a devil's head?' as visions of viruses flashed though my mind. 
 
I finally figured out that it showed up right after a Win7 scheduled system update.  So i shut off system updates and never looked back.
 
But then found that i had a thousand system updates to get done so i temporarily allowed system updates and the dirty rapport got back in.  So your program has already paid off microapp - but it may not be related to my present problems with Certain plugins - I am about to try.
 
I will also unload a bunch of data from the program drive C: because it is past 3/4 full.
 

Twice now I have upgraded an old but decent video card and seen significant performance improvements in SONAR. Like, serious changes for the better.
 

I would also really recommend running the latest firmware and drivers on your RME card. I love the UCX by the way, I have one too.

It's funny - the audio continues, while the Sonar GUI screen stalls and response from mouse/key clicks is greatly delayed. 

 
The only time I've ever seen anything like this was when I had inadvertently hit the pause key on my keyboard.

I have had a similar issue like this and it turned out to be a rogue plugin that didn't like the 64 bit double precision engine. You could try turning it off under edit/preferences/driver settings. If this fixes it then it will be a case of hunting down which plugin doesn't like it.
If it doesn't then it could be just that you are running close to the maximum your system can handle. Neutron is pretty heavy on CPU especially if you stack up instances of it.
I currently have a 72 track project with around 10 separate instances of Neutron running ( as well as a number of other plugs) and it is just clinging on by its fingertips

This thread:
http://forum.cakewalk.com/Solved-iZotope-Neutron-and-SPLAT-problem-m3494484.aspx
 
says there is an issue with the VST2 Neutron and that you should use the VST3.
 

Rapport Management service is installed by a program called Trusteer which provides secure communications between companies (like banks). Is this something for your work ? If not, see if Trusteer is installed and uninstall it.

My next move on this problem would be to run CCleaner and Malwarebytes. It sounds like the OP's system is bunged up with all sorts of stuff. Get all the updates done, check the system with Malwarebytes and finally clean it all up with CCleaner. IT's all available using free versions. After all that is done run the DPC monitor again to see if there are improvements. 
If there's something installed on my system and I didn't put it there, I kill it. Of course that's after I've ensured that it's not a system driver.

ampfixer
My next move on this problem would be to run CCleaner and Malwarebytes. It sounds like the OP's system is bunged up with all sorts of stuff. Get all the updates done, check the system with Malwarebytes and finally clean it all up with CCleaner. IT's all available using free versions. After all that is done run the DPC monitor again to see if there are improvements. 
If there's something installed on my system and I didn't put it there, I kill it. Of course that's after I've ensured that it's not a system driver.

CCleaner is prob a good idea. Be careful with it tho. I usually only use it to remove unwanted registry items. Malwarebytes should be run periodically at least once a month if not more often.
I also look at the running services and installed programs and kill anything I did not specifically install (after investigating of course).
If you use the DAW PC for other things, all the above should be done religiously.