We are heavy Google Calendar users in our family and it has always bothered me that there was no visual cue between weekdays and weekends on ‘Week’ or ’7 Days’ view options. If this bothers you as well, simply edit the userContent.css file for your respective browser and add the following:

/* bluegrey weekends on gCal. */
td.tg-weekend {
    background-color:#F0F8FF;
}

The result is a pleasant distinction as the 7 day window moves forward.

The file userContent.css sets the display rules for web content and is located in the sub-folder called chrome in your profile folder. This folder does not exist by default, so you may need to create it before you can start adding your preferences. On my Macintosh, the chrome folder may be found:

% pwd
/Users/kunau/Library/Application Support/Firefox/Profiles/j2am41kw.default/chrome
 
% ls -al
total 24
drwxr-xr-x@  5 kunau  kunau   170 Nov  5 18:44 .
drwx------@ 70 kunau  kunau  2380 Jan 11 11:00 ..
-rw-r--r--   1 kunau  kunau  1039 Nov  5 18:44 userContent.css

It is a little thing, but it makes all the difference.

(See also: Mozilla.org: Customizing Mozilla)