Ok so i found the file.

"/usr/share/applications/defaults.list"

so for the gif image to open in web browser to need to add a line in web browser one and delete gif association with image viewer.

root
vi /usr/share/applications/defaults.list
OR if you have leafpad or any other text editor(just change leafpad to you text editor name) installed
leafpad /usr/share/applications/defaults.list

add the following line in browser supported mime types section
image/gif=hildon-browser.desktop

and in image viewer section delete the following line
image/gif=image-viewer.desktop

save the file and you are good to go.