What extensions are a problem for you? Firefox 43 requires that extensions be digitally signed by the Mozilla Add-ons team. This is a security measure. Some publishers are still in the process of getting their extensions signed. If there are no updates for your unsigned extensions, and no workable signed alternatives, you can make a temporary exception to the signing requirement until they get updated. This is global for all extensions, there's currently no way to only make an exception for one specific extension. (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter/Return. Click the button promising to be careful. (2) In the search box above the list, type or paste '''xpin''' and pause while the list is filtered (3) Double-click the '''xpinstall.signatures.required''' preference to switch it from true to false -- note that this is for '''Firefox 43 only''' ---- As an aside, you can find official copies of earlier versions of Firefox from a link in this support article: [[Install an older version of Firefox]]. No need to use third party sites.