User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0 Build ID: 20161208153507 Steps to reproduce: 1) I mount a remote directory into my local file system on Linux using SSHFS. Sometimes the mount command succeeds but the directory is inaccessible for a period of time and needs to be remounted. 2) After the first (possibly unsuccessful) mount command I launch Thunderbird. 3) At some point after that I remount the remote directory using SSHFS and verify that its contents can be accessed. 4) After some time (minutes/hours) I try to attach a file to an email I'm composing. Actual results: At step (4) above the Attach File(s) dialog box comes up but it's not functional. I can select folders in the panel on the left but the panel on the right is not populated with their contents. I also cannot enter any text into the Location: text field. In order to successfully attach files I have to restart Thunderbird. Expected results: The Attach File(s) dialog should be functional and let me select files to attach.