For several firefox add-ons I have successfully used a hack I found somewhere to be able to install them in Minefield, although they were officially not supported. It works like this: download the .xpi file, open the install.rdm inside this archive in gedit and change the max. version parameter to 3.3. Then open the .xpi in Minefield et voila, it installs. This worked for me for 'searchload options', 'tiny menu' and 'add to searchbar'. Of course, it is a dangerous method: if an add-on is really incompatible with Minefield it may screw it up. But if it is labeled incompatible just because it has not been tested yet, it works fine.
Now I tried this with the cooliris beta for linux (formerly known as piclens), but when trying to open the adapted .xpi Minefield complains it could not install,
"because: Signing could not be verified.
-260"
Is there a workaround for this, or is this add-on truly incompatible with Minefield? And what does this "-260" mean? Thanks in advance.