Use a browser link, looking up excessive amount (7)
I believe the answer is:
surfeit
'excessive amount' is the definition.
(I've seen this before)
'use a browser link looking up' is the wordplay.
'use a browser' becomes 'surf' (I've seen this in another clue).
'link' becomes 'tie' (tying is a kind of linking).
'looking up' is a reversal indicator (in a down clue, letters go up).
'tie' reversed gives 'eit'.
'surf'+'eit'='SURFEIT'
(Other definitions for surfeit that I've seen before include "Overindulge" , "excessive amount" , "having had quite enough" , "it's more than one needs" , "Superabundance" .)