Wirtschaftsuniversität Wien Magisterarbeit - SemanticLab

6.1.6. Accessing SQLite databases
Although the developed extension does not use SQLite databases, the topic should be
briefly discussed for the sake of completeness. SQLite databases have been introduced
with Firefox 3.0. They are easy to handle and can be queried using SQL. By using the
mozStorage API one can directly open a connection to the database and query it by
using JavaScript. The results can then be used to create XUL elements or simply by
building content via JavaScript. [MDC09j] provides an example and more details.
6.1.7. Accessing the local filesystem
Once installed, an extension runs in the scope of the Firefox browser and has therefore
much higher rights on the user’s computer than for example websites which are visited
by using the browser. That means that extensions can access (and therefore also delete)
all files and directories, even recursively! [MDC09k] provides a good overview about the
API and how to use it, including some working examples.
6.1.8. Using a integrated development environment (IDE)
The author strongly recommends using an IDE such as Eclipse to develop Firefox extensions.
It makes the development process a lot easier, for example by using Subversion
(for version management) and Ant to automatically build the xpi-files. There are tools
such as XulBooster (an Eclipse Plugin) 1 , the “Extension Developer’s Extension” (a Firefox
Extension) 2 or the “Firebird/Thunderbird Extension Wizard” 3 available which also
help in setting up a proper environment.
6.1.9. Debugging Firefox
For debugging Firefox extensions, one needs a JavaScript debugger such as Venkman 4
which is Mozilla’s official JavaScript debugger. Although it provides useful insights,
it sometimes cannot help developers, for example, finding out why extensions are not
installed properly or why components are not loaded. This is due to the fact that
Venkman itself comes as an extension and therefore is loaded the same time as other
extensions are loaded and therefore cannot interrupt start-up processes. To accomplish
this, developers have to run Firefox in debug-mode and set breakpoints in the Firefox
source-code itself. More information on that issue can be found at the MDC. Another
very important tool for debugging Firefox is a DOM Inspector. A DOM Inspector such
as “DOMi”, Mozilla’s DOM Inspector 5 , lets you inspect the document structure of XUL
windows and the browser. It is for example very useful to find out how to address XUL
elements if the documentation is not clear in that point.
1 http://cms.xulbooster.org
2 http://ted.mielczarek.org/code/mozilla/extensiondev/
3 http://ted.mielczarek.org/code/mozilla/extensionwiz/
4 https://developer.mozilla.org/en/Venkman
5 https://developer.mozilla.org/en/DOM Inspector
57