Question Why X-Firefox does not keep the cache of visited sites?
Answer Due to obvious space saving request on Your flash drive and to avoid a phisical wear down of it, with continuous read/write operations, made by your profile cache folder, X-Firefox sets the cache folder into a temporary directory onto host hard drive, and deletes these data each time the program is closed.
The cache temporary folder is:
%TEMP%\X-Firefox\Cache\Default\Cache (C:\Documents and Settings\USER\Local Settings\Temp\ X-Firefox\Cache\Default\Cache)
In fact, if You open user.js file, containing all X-Firefox settings and located in X-Firefox_X.X\ User\ Firefox\ Profiles\ Default, You can see the cache related string is: