[Note: I characterized this question as an "Installation and updates" issue (even though it is not ''per se'' about initial installation or updates) because moving a profile involves installation issues.] Recently I moved my TB profile, for the second time in the past few months. This time I paid closer attention, and noted several things of interest (that may touch on some questions that remain undiagnosed in this forum): # TB took longer to start up, as it could find none of the folders cached in folderCache.json, so rebuilt the cache from the new profile location before starting. (I only learned about this from the next effect.) # The "Move to" "Recent" folders list was empty; this cached list only gets rebuilt from use (that is, from moving messages manually (not via filter) to destination folders). This effect led me to [https://support.mozilla.org/en-US/questions/1378700 folderCache.json]- and also may suggest why the OP in that question could not get resolution of his problem. # The newly cached folderCache.json was 528 KB, compared to 365 KB at the old location -- and that, in turn, was 170 KB larger than the 195 KB size of folderCache.json at the original location. So each time the cache is rebuilt it grows perhaps 150~200 KB (size depending on the many-times-repeated path length). What causes the file growth? Because each time it is rebuilt, TB checks through all of the cached folder paths, apparently guided by the mailboxes listed in folderTree.json (see image below). [I ''think'' TB just checks each path to see whether it is compatible with the current profile location. If yes, the path is cached for runtime; if no, the path is repopulated from the current profile location (which takes most of the startup time).] But ''TB never deletes the no-longer-valid paths''; it just appends to what was already in the file, so that '''''the list of cached folder paths just grows''''' (thereby increasing TB's startup time, every time). The best way to get rid of the old stuff is just to delete folderCache.json and let it rebuild on the next startup, to reduce the time needed for subsequent starts. Finally, my questions: In addition to folderCache.json (different timestamp in each profile, of course), there are four files which are the same in all profiles: folderCache-''x''.json, ''x''={1,2,3,4} (see screenshot). These are apparently from actions prior to the profile relocations, as they are simply copied from one profile to the next, unrelated to changes in folderCache.json. Can someone tell me: # What actions cause the creation of folderCache-''x''.json files? # Why folderCache.json merely appends new folder paths without deleting the old ones? # Why folder paths are specified explicitly (fully qualified) rather than relative to the profile path? Thanks for any pointers.