Firefox 4.0 beta releases are a snapshot of the current development stage of Firefox 4 and meant for testing by experienced users.<br /> If bugs are found then they can get reported and fixed before the final 4.0 version gets released.<br /> Not all website work properly with the Firefox 4 beta versions and nightly builds.<br /> If you do not have experience with such test releases then it is better to stay with Firefox 3.6.x releases. See: * [[Web sites or add-ons incorrectly report incompatible browser]] * http://kb.mozillazine.org/Resetting_your_useragent_string_to_its_compiled-in_default Check the <b>general.useragent</b> prefs on the <b>about:config</b> page.<br /> You can open the <i>about:config</i> page via the location bar, just like you open a website.<br /> Filter: <b>general.useragent</b><br /> If any <i>general.useragent</i> prefs are bold (user set) then right-click that pref and choose <i>Reset</i>. ---- Create a new profile exclusively for the 4.0 beta version and create a desktop shortcut with -P "profile" appended to the target to launch that profile. * http://kb.mozillazine.org/Testing_pre-release_versions * http://kb.mozillazine.org/Creating_a_new_Firefox_profile_on_Windows * http://kb.mozillazine.org/Shortcut_to_a_specific_profile * http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox