Fiddler is a great tool & Composer an excellent feature of it. I frequently have to reboot my dev. PC for various reasons (actually it crashes a lot) and loosing my Composer URL history is a painful consequence. Could the URL history be retained between invocations? I use a set of about a dozen different endpoints frequentl, so a history size of 12-20 would likely be enough.
It would be even better if the last used request header and/or body and/or type (POST/GET/..) and/or Protocol (HTTP/1.1 etc.) for each URL could also be saved but perhaps that is asking too much.
Bless you for making this tool.