User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b11) Gecko/20100101 Firefox/4.0b11
Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b12pre) Gecko/20110214 Firefox/4.0b12pre
The font cache size is always shown as n/a unless firefox.exe is elevated (administrator). Since most users (I think) don't run Firefox elevated (would be a security risk), there is no point to display it in about:support.
Once MS fixes the underlying bug there's no reason to display font cache size. We could simply omit the string altogether if not available (i.e. rather than "n/a") but I'd prefer not to eliminate it entirely since it can be useful when it is available.
Nothing wrong here, maybe the line should be hidden if the value is "n/a" but why would you hide a field when it's possible to see it?
Now that MS has released a patch for the underlying problem, the plan is to remove the font cache size information. Probably for a .x release.
Created attachment 526653 [details] [diff] [review]
patch, trim out font cache size
Pushed to trunk