Thanks to Fabrice Desré and Wladimir Palant, development builds of AdBlock Plus support Fennec! The port embraces Fennec’s minimalistic design asthetic – exposing only a simple options UI. However, this is more than enough to make a great impact on browsing in Fennec.
Besides reducing the visual clutter on web pages, ad-heavy pages load noticeably faster! As Wladimir notes in his post, AdBlock Plus will only work in nightly builds of Fennec (version 1.0b6pre). Install a nightly version (including desktop versions) or use the new nightly update channel from your Maemo device. He also mentions that work to improve the first-run experience is coming in future releases.
Install a development build of AdBlock Plus by navigating to https://adblockplus.org/devbuilds/adblockplus/ using Fennec and click on the most recent XPI file. Fennec will step you through installing the add-on.