+++ This bug was initially created as a clone of Bug #737642 +++ Panorama (browser/components/tabview/thumbnailStorage.js) makes use of nsICacheService::OpenCacheEntry, which may block on disk I/O. nsICacheService::AsyncOpenCacheEntry should be used exclusively. (We, the Necko team, would like to remove the nsICacheService::OpenCacheEntry method sometime soon.)
Will be fixed by 745303.
Does that mean that Panorama will not use the cache API at all?
Yes. Though the thumbnail service currently still uses it. But we're fixing that, too.
Fixed by bug 745303. Panorama doesn't use the cache API anymore. The thumbnail service still uses it asynchronously but we're moving away from the file cache in bug 744388.