One of the goals of the experiment was to replicate the behaviour of an old VGA game I’d coded 12 years ago: the player controls a character that moves across the screen, showing a nice photograph. When player reaches a percent of completeness, the level is finished and game starts on the next level.
The old VGA game used memory buffers to create the effect. canvas element doesn’t use pixel buffers neither anything similar but vector graphics. Instead of pixel masks, you must indicate mask shape with commands. So, to achieve the effect, my solution was to create one mask by each horizontal line, so I could take the control of how much surface was cleaned.

var screen = [320,200]; // screen dimensions

var limit = [] // control structure of the masks

// limit assignation
for(var k = 0; k < 0; k++) {
limit[k] = [mask.min,mask.max]
}

The main drawback of this approach is that browser has to redraw each mask line on each frame, so it can be very slow on old (and a few newer) machines.

Code for this and other canvas related experiments.

The project running in its current state at the Google App Engine.

• Geany. Lightweight text-editor with many useful plugins. Cross-platform.
• NautilusSVN. Nice set of SVN (version control) scripts for Nautilus, Gnome navigator. It tries to mimetize TortoiseSVN for Windows.
• Meld. Diff utility. Complements SVN functions with a nice file differences display. 
• and Firefox.

Also I use different virtual desktops for each application. I lose javascript code completion, but I’m yet used to work without it!

Recently I'd serialized a form with jQuery :

var params = $("commentForm").serialize(); // get a string with form parameters

then I use it in a generic ajax call:

$.ajax(
   method: "POST",
   params: params,
   ….
);

Too normal until debugging the result of the query in Firebug. The server's answer contains the params of the form:

Array(
   id:4893
)

But firebug window shows:

Array(
   id:0
)

Different results. Why? Firebug does not capture Firefox query. Instead of that, it replies the query without the parameters. So it can show wrong results to developers who are debugging their ajax posts.
I have noticed that behavior in Linux and formerly in Windows with different versions of Firebug, so don't trust it!

Setting a develpment enviroment:

For Ubuntu:

To run more than a single firefox instance:

/usr/bin/firefox -no-remote -P dev

“about:config” settings:

javascript.options.showInConsole = true
nglayout.debug.disable_xul_cache = true
browser.dom.window.dump.enabled = true
javascript.options.strict = true
extensions.logging.enabled = true

Profile extension folder: ~/.mozilla/firefox/[profile name]/extensions
where [profile name] = name of the profile, usually with prefix generated by Firefox.

Extensions are ZIP compressed files, but to develop using a more convenient folder structure:

• Create a file in the profile extension folder with a GUID or your mail as name.
• Write the absolute path of the xpi package as content.

Extension Wizard to generate skeleton: http://ted.mielczarek.org/code/mozilla/extensionwiz/