Can anyone else recreate this? I've recreated it on two SLED 11 SP2 machines with two different users.

In Firefox go to the Add-ons page then click 'Get Add-ons'. Searching for anything always brings up no results. Even searching for Add-Ons which are featured on the 'What are Add-ons?' page.

E.g. When I looked at the 'What are Add-ons?' page an Add-On called 'Thumbnail Zoom Plus' was listed. So I put 'thumbnail' in the search field and got no results. I went back to the 'What are Add-ons?' page, clicked the link for Thumbnail Zoom Plus' and installed it. So the Add-On is compatible with the version of Firefox in SLED SP2.