Am developing a site using drupal 7.15 I am having problems with displaying a ddblock in internet explorer and I think it may be due to too many css files. If I aggregate them can I continue to edit them? Also, can I still use Firebug to view my css? All the posts I read seem to refer to setting aggregation when you decide to "go live" Sorry to ask such an elementary question.
You can still edit the original files as much as you like, but you won't see the changes reflected in the front end until you clear Drupal's caches.
You can absolutely still use Firebug to inspect your CSS, but keep in mind that the files have been aggregated, so you won't be able to pinpoint the original file and line that a rule comes from.
That's pretty much why it's recommended to keep aggregation off during development, unless of course you're testing the aggregation itself.