List of my favorite Firefox 4.0.x compatible extensions:


Extension Official Page
adblock_plus-1.3.6 link
add_bookmark_here_2-4.0.20110331 link
betterprivacy-1.50 link
bugmenot-2.2 link
cookie_monster-1.0.5 link
copy_link_name-1.3.2 link
copyurlplus-v1.3.2 link
cutyfox_url_shortener-1.4.1 link
dictionarysearch-4.0.1 link
downthemall-2.0.2 link
extended_copy_menu_fix_version-1.6.1c link
extended_statusbar-1.5.7 link
firebug-1.7.0 link
firessh-0.85.1 link
flashblock-1.5.14.2 link
flagfox-4.1.2 link
fox_to_phone-1.1.1 link
ghostery-2.5.3 link
gmail_manager-0.6.4.1 link
gtranslate-0.8 link
instantfox-1.6.3 link
jsview-2.0.5 link
liveHTTPheaders-0.16 link
menu_editor-1.2.7 link
Print_pages_to_Pdf-0.1.8.5-LIN link
printpdf-0.76 LIN - printpdf-0.76 WIN link
quickJava 1.8.0 link
read_it_later-2.1.1 link
regular_expressions_tester-3.2.11 link
right-click-link-1.1.5 link
ShareMeNot-1.0.0.2 link
sqlite_manager-0.7.1 link
tab_mix_plus-0.3.8.5 link
too_many_tabs-1.3.3 link
user_agent_switcher-0.7.3 link
web_developer-1.1.9 link