For just a few kilobytes, I would not worry. But if you are,

Location of the cache/cache2 folder; Windows: *C:\Users\<user>\AppData\Local\Mozilla\Firefox\Profiles\<profile>\ Mac: ~/Library/Caches/Firefox/Profiles/ Linux: ~/.cache/mozilla/firefox/

Close Firefox. Open your file browser to the above and remove the folder.

Thanks for your response.

I did that, but opened firefox again, and it shows 55kb in cache, and the cache2 folder has appeared again.

I just wondered what it could be, and if it can be anything malicious?

As I said, don't worry about it. Any missing files Firefox needs it will recreate.

Note that you can check via the about:cache page what content this is about. This could be about OCSP responses or or other data uses internally.

Thanks for the replies.

I looked in about:cache, and there as oscp responses and various mozilla stuff.  :)

I also noticed the total storage space of files in cache2 folder was 58.4kb, but in the bit where you can clear 'cached web content' in preferences, it is 63kb, and in about:cache in 'disk' it is 63KiB". Just wondered why that would be? When I convert kb to KiB it's not the same amount.

Thanks if anyone knows :)