My point was, unless you are force closing your browser than what difference does it make? For most people the settings are remembered because they don't force close their browser. My settings were even remembered after powering off and back on.
Ok I have no real agenda here except that it isn't working that way for me so I 'm going to outline what I did to test this just so someone can point out what I'm missing.
I use cbs.com as a test because A) they redirect mobile browsers to m.cbs.com and B) they don't have a link to view the full site. And C) they don't support flash in the mobile site.
1. I go to cbs.com and get redirected to m.cbs.com
2. I use about:debug to get the advanced settings
3. I set the UAString setting to "desktop"
4. I go back to cbs.com and it shows me the full site, flash works.
5. I rebooted my device (I was force closing, but I used a reboot to match your experience)
6. I loaded my browser and went back to cbs.com and was redirected to m.cbs.com
7. (Checking the settings I am no longer in debug mode) I do about:debug
8. I go to cbs.com and it redirects me to m.cbs.com. I go into settings and check the UAString and it is set to "desktop" I click on "desktop" option again.
9. I go to cbs.com and it displays the full version.
On my phone it appears that while the UAString remembers what I set it to the debug mode gets reset when the browser gets unloaded and I have to go back in and set it every time the browser reloads. This happens even without turning off the phone or doing a force stop. The browser gets unloaded after being inactive for a while and I have to do the same procedure.