This is how you can do:
1. Download Pencil-1.2-0-fx.xpi
2. Rename to Pencil-1.2-0-fx.zip
3. Open or extract Pencil-1.2-0-fx.zip with your favorite zip-
4. Open the file install.rdf in an ordinary text-editor
5. Change the text em:maxVersion=”3.6.*” to (for example)
(it’s this tag that prevents Firefox 4 to install the extension)
6. Save the file
7. Save or re-create (depending of your choice in point 3 above)
8. Rename Pencil-1.2-0-fx.zip -> Pencil-1.2-0-fx.xpi
9. Open Pencil-1.2-0-fx.xpi in firefox 4 and it should be installed
without (I’ve tested quickly using Ubuntu 10.10 & Firefox 4)
Once again – this is a current workaround until a new official version
has been released.
I would also, as always, thank the developers for a great product!!