When I enter a search string for both yahoo or google (but not as yet duckduckgo) somewhere the string is "edited" before it is sent and all extended search characters deleted so "field1 field2" and "field1 -field2" return identical results. Some of the editing can be seen when the text is transferred from the search window to the address window. for example my try at ' "-"field2' was edited to '- field2' with a space between '-' and "field2". I am running Linux Mint and have done a Firefox update with no effect. Note that this not how it used to behave.