Firefox 4 is considered unsafe and is no longer supported, you may however revert to Firefox 3.6 which is (for now at least) still supported. '''It is possible to use the Google Toolbar in Firefox 5,''' if you download, install, and use an add-on [https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter/ compatibility reporter] Google has stopped supporting Google Toolbar with Firefox 5, many of its features are already available on Firefox. You will find further discussion and links in other threads such as: [[/questions/837142?page=3#answer-215143]] which will include links to Googles own information. In due course a Firefox KB article is likely to be written explaining the situation. [/forums/knowledge-base-articles/707162]