CCleaner loads slow when large Firefox cache

When loading ccleaner, there's high disk activity when firefox cache is large, even when I unchecked everything in the applications tab (seems like ccleaner still loads the directory structure from $mft). Is there a way to change this? Maybe a way to remove firefox from the applications tab?

For the sake of curiosity how big is the Firefox cache?

You can decrease the cache size limit in Firefox if you've modified it to use a non-factory default amount, or have Firefox itself clean the cache when exiting it, maybe that would help.

unable to recreate this using caches of 0.5-2.0Gb. FWIW I'm using the new cache backend though, so MMMV

It's set to auto, now using 400MB with 20k+ files. I think it's caused by loading the directory structure from MFT, because if I run folder properties on the cache folder before ccleaner, it loads a lot faster.

Clearing the cache works, but I want to keep the cache. If I move the cache folder away then run ccleaner, it's fast. But it's slow again if I move the folder back in.

What's the new cache backend? I tried adding browser.cache.use_new_backend in firefox 26 and it doesn't seem to work.

The new cache back end is only in Firefox 28 and newer I think. 27 beta might have it but I don't recall