So you can record any sound from your browser or any other software.
Next step will be find the produced file and convert it to mp3 if it's recorded in any other format and i want to use it on my mp3 player. Probably on settings you can choose audio format to record sound, i didn't checked this time. Audacity is around since a lot of years, and more, and always been usefull.
http://manual.audacityteam.org/man/tutorial_recording_computer_playback_on_windows.html
Download: http://www.audacityteam.org/
Once we decide to stop recording the audio we are listening threw computer speaker, we can go to Fiel menu and select "Export to" and pressing on Type of output we can select mp3 format and many other sound file types :-)
And we can add some metadata like author, year, album title and so on...
oops!!! i forgot, we need lame_enc.dll to export to mp3.
About download: http://manual.audacityteam.org/man/faq_installation_and_plug_ins.html#lame
Lame_enc.dll is here: http://lame.buanzo.org/#lamewindl