Is this a new installation on Windows 10, or did you upgrade your existing Firefox installation from an earlier version of Windows? Assuming this was an upgrade, maybe it's this: Due to a change in how Firefox 39 associates keywords with bookmarks and/or history, the address bar is newly sensitive to corruption in the database that stores your history and bookmarks (the places.sqlite file). This will be fixed in Firefox 40, due out next week, so if this is the problem, you have a couple different options: (1) Immediate workaround is to remove/rename the places.sqlite file, but then you lose all your history, so that's really not very attractive for people who rely on history for revisiting sites. If you decide to try that, please see this thread for the detailed steps: https://support.mozilla.org/questions/1073204 (2) You could install Firefox 40 during its last week of beta testing. Firefox 40 has numerous compatibility fixes for Windows 10, so this might be the better thing to try. If you decide to try that, please see this thread for the detailed steps: https://support.mozilla.org/questions/1076158 ---- If this was a new install of Firefox, please try Firefox 40 (option 2 above).

You can try to check the places.sqlite with this extension: *Places Maintenance: https://addons.mozilla.org/firefox/addon/places-maintenance/ *http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox *https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file