Most mistakes web designers make stem from the assumption that the way they are seeing the site in their web browser is the way everyone else sees it. By using uncommon defaults in your web browser, you can ensure that you have left to the default only those aspects of a page which you had intended. I call this "misconfiguring" because it is intentionally configuring a web browser to display pages wrongly. If the page looks correct with such settings it is probable nothing has been left to chance.
It is common practice to test a web site in various web browsers, but this testing can give a false impression of the compatibility regarding different default settings. This is because almost all browsers have settled on a common out-of-the-box set of defaults. The user is allowed to override these defaults. Fail to anticipate this and your website risks visual problems for some users (perhaps 1% or so, to take a wild guess). Problems include:
- Character set issues, such as Â£ or the opposite, a broken character symbol (the question mark diamond in Firefox) rather than £.
- Specifying a font colour but not a background colour, causing clashes or even invisible text. Perhaps 10% of websites fail to specify a page background colour but assume that it will default to white.
- Linking images which are intended to composite onto white. This looks dreadful onto most other colours.
- Copy looking illegible due to tiny serif fonts (sans-serif is more legible on low-resolution screens).
- Body font clashing with image-based buttons and titles: serif and sans-serif fonts rarely mix.
- Pale-coloured boxouts. What appears pale is in fact a function of the background colour. A light pink box appears pale on a white background, but very bright on a black background, for which the corresponding effect would be a dark red box.
The browser defaults which you may want to change include
- Character set
- Background colour
- Text colour
- Font style
- Font size, although in theory you should avoid specifying this for accessibility reasons.
Misconfiguring a web browser is an art. It is perfectly acceptable to use the defaults a user specifies, as long as all of them are respected. While you should feel free to wholly b0rk a browser which you use purely for testing, it is more beneficial to misconfigure the web browser that you use for primary development. For me, this is the same web browser that I use for everything else, Firefox. Therefore the misconfiguration has to be something that isn't wholly unusable to me. More importantly, the new defaults have to be ones that I would be unlikely to use for a website, otherwise I could still rely on my defaults.
Because I tend to use sans-serif fonts, white backgrounds and black, grey or blue text, and UTF-8 character set, my browser is set to default to serif, coppery-orange text on a mid-grey background. I'm experimenting with ISO-8859-11 (Thai) as my default character set, because this isn't compatible with UTF-8 nor ISO-8859-15 for the most common problem area: £ and € symbols. It is compatible for ASCII-range symbols, so try UTF-16 if you are aiming for perfect incompatibility. I don't specify font-size but I Ctrl-roll my mousewheel on occasion to watch how the site changes at different font sizes.