When attempting to install the "TryAgain" add-on (https://addons.mozilla.org/en-US/firefox/addon/2462/) I receive the error message "Firefox could not install the file at https://addons.mozilla.org/en-US/firefox/downloads/latest/2462/addon-2462-latest.xpi?src=addondetail because: Invalid file hash (possible download corruption) -261." In an attempt to resolve the problem, I followed the instructions for "Unable to install add-ons" in the support Knowledge Base, specifically the section titled "Corrupt extension files" (https://support.mozilla.com/sq/kb/Unable+to+install+add-ons#Corrupt_extension_files). After restarting the browser as directed, the add-on ("TryAgain") was still unable to be downloaded. Also, when I checked my currently installed add-ons, I found that some were now "Not compatible with Firefox 3.6.8" - they had worked before deleting the files and restarting the browser, and their download pages currently show the add-ons as being compatible with my version of Firefox.