This is a request for a "simple CSS editor". It wouldn't expose the language, but rather would generate a stylesheet. The base of this should be the settings in the NN4 Appearance Tab. The ability to ignore BLINKs would be nice too. =) The CSS editor could be used to edit or create a new user style sheet, or edit a CSS file similarly to the editor. Of course, it's difficult to take an arbitrary CSS stylesheet and convert it into these prefs, so it might be save-only for files, and you'd need to keep user stylesheets in both forms.
Bug #17534 is about a full CSS editor. Not sure whether this bug is a Browser or Editor thing, BTW.
Putting on correct component and setting QA contact. firstname.lastname@example.org - instead of using the Browser-General component so often, please check out: http://bugzilla.mozilla.org/describecomponents.cgi?product=Browser when writing a bug and try to get on the correct radar on initial submit. This could speed up things a bit for ya. :-)
Funny... It seems to me that Bug 17534 is a simple css editor (just some syntax checking and highlighting) while this bug is in fact a request for a full-fledged css editor (GUI only, no exposure of the code). I agree with you: "it would be nice if..." but I'm not sure we want to commit to that business even more. Closing as Later.
Consider this request as just a bunch of controls, like you have with the NN4 appearance page (eg default page colours). There might be a few checkboxes like "don't allow blink". I don't know how you could do CSS without exposing the code, but however you do, this isn't a request for it.
The current plan is to let users add "!important" rules in ua.css (like minimum font sizes for visually impaired people, specific color sets for color-blinds or... no blink for epileptics). The problem is to figure out what other settings could be of interest for enough people to justify a GUI.
reopening my LATER'd bugs
Reassigned to Daniel (fyi only)
This is a RFE for the 3rd step in the CSSization of Composer . Its purpose is creation and manipulation of stylesheets in Composer. This is not too hard to do but implies a lot (really a lot) of UI design and work.  http://www.mozilla.org/editor/adding-css-to-editor.html Accepting Bug :-) (does not mean I'm going to work on it right now tho) See also bug 77705 (step 2) and bug 16255 (step 4).
We don't need anything fancy until we implement bug 6782 "UI for alternate and user stylesheets".
*** Bug 34837 has been marked as a duplicate of this bug. ***
milstone bulk change
Created attachment 78540 [details] work-in-progress screenshot 1 Here is a first screenshot of my Stylesheet management dialog. I am working on it on my personal time, so no ETA. Everything there is subject to changes and even complete rewriting, so don't focus on string or design choices.
Changing QA contact
Related products of interest : Westciv's StyleMaster http://www.westciv.com/style_master/index.html Westciv's LayoutMaster http://www.westciv.com/layout_master/index.html
CaScadeS project requested on Mozdev ; XPI will be available from there as soon as I get the account.
Added an expert mode toggle in the dialog : - in expert mode, all creation buttons (sheet, rule, @media, ...) are enabled depending on the selection in the sheets/rules tree. The user cannot create a rule w/o having a sheet first. All kind of selectors are available - in "not expert" mode, only the rule button is enabled. Creating a rule inserts it in the last embedded sheet in the document, and even creates a sheet if needed. User cannot create media-based stylesheet nor other complex css stuff. CSS rule creation offers to create "named styled rules" (class attribute) or "element-based rules" (type element selector)
all work visible at http://cascades.mozdev.org/ starting from now
fixed by CaScadeS landing in mozilla/extensions/editor/cascades (was bug 161663)