Why is there only a spell checking capability in the main body? Why not the title and the edit summary field too (if you are editing a question)?
Because the title is
<input id="title" name="title" type="text" maxlength="300" tabindex="100" placeholder="What's your bug, feature request, or meta-discussion topic? Be specific." class="ask-title-field" data-min-length="15" data-max-length="150">
and the text is:
<textarea id="wmd-input" class="wmd-input" name="post-text" cols="92" rows="15" tabindex="101" data-min-length=""></textarea>
and FireFox only check text areas for spelling errors.
To change that behaviour open an
tab, filter for
layout.spellcheckDefault, double click the value and change it to
Spellchecking isn't something done by the website but rather something done by the browser.
The main body is a single
<textarea> which browsers typically assume will be used for composing long blocks of text and enable basic spellchecking automatically. The title and edit summary controls are instead
<input type="text"> fields and browsers typically do not enable spellchecking for them.
On a related note, the HTML5
spellcheck attribute can provide browsers with a hint as to which controls should have spellcheck enabled. This table shows the browser support for this attribute.