Fx - script is installed by GreaseMonkey addon for userscripts (in older Firefox Scriptish addon may be used);
Chrome|new Opera(15+)|Vivaldi|Yandex browser - immediately (on the page chrome://extensions/ it placed as unpacked script in "developer mode"; directory sholuld be contain manifest.json or JSON code lower, rename script: "GoogleSearchExtra_Buttons.user.js" or similar if need; or by other methods - Tampermonkey);
Opera 12- - save userscript in file placed in Opera directory... ( there are instructions );
Script adds 8 types of buttons that doubled links hidden in:
change interface language (en(default), fr, ru, de, es) in Settings area; small sticked appearance;
search PDF docs;
search in site (from list; if no list in settings (or commented), this button is not displayed);
write list of your favorite sites in code (example: ['slashdot.org','digg.com']);
search in interval of dates (fast opening of Google inteface);
search for 1,2..13 last days;
search for 1,2..10 last weeks;
search for 1,2..11 last months;
search for 1,2..10 last years;
search for 1,2..22 last hours;
save of each select in ext. localStorage;
multilanguage interface by settings in navigator.language or in script: ('en' is default or on undescribed language);
remove lang in settings (select "en w/o hints") for no hints (interface language will be English);
save settings (language and sites list) in the external localStorage (google clean own storage), copy list as text;
keep type of current page ('tbm=' parameter) - news, pictures, video etc.
2018-12-11: White-Mint-Oval design (as default), blue old design as additional;
2018-12-05..11: start page with buttons is repaired; fix img search; hide buttons in shop|boks|finance;
2018-11-30..12-4: search by up to 30 filetypes; images search by types and Show Sizes checkbox;
2018-11-19..20: by changes of layout (classes and logic) of results page (TODO start page), external localStorage is placed to Google domain (gstatic.com)
2017-12-12: transitions in fading columns; some style modifications
2017-11-13: temporary save option "sort by date" for nexr search in the same page
2017-03-11: more contrast gray design of extra buttons
2017-02-04: fix white-on-white border of input field
2016-12-12: gray design of buttons on the pages with new desing of Google; setting of return to old buttons design.
2016-12-07: fixes for compatibility of new design of input fields; old format is supported also.
2016-01-17: fix autostart after select of site; switch of checkbox.