- Downlowd Venkman 0.9.85.
- Change file extension to .zip and unzip.
- Open install.rdf with your favourite text editor.
- Find <em:maxVersion>1.1</em:maxVersion> and change the maxVersion to 1.5 (or any arbitrary number higher than 1.5 – it might or might not work on future releases of FireFox).
- Save your changes and close your text editor.
- Rezip the files and change the file extension from .zip to .xpi.
- Open the new XPI file in FireFox (using File | Open File menu or just drag-and-drop).
If you are a brave and trusting sort of individual, you can just download my modified XPI here: Modified venkman-0.9.85.xpi (209.03 KB).