Ie does not have the ability to open .zip files. It will normally use the built in zip function, automatically, through the correct path. You seem to have lost this associate.
There are two ways which might fix this. One is to right click and choose the "open with" option and browse. Here you can select "7" or IE. (Make sure you have the box ticked, bottom left). The latter choice may be once again lost when you try to unzip files throu FF.
The second method is to open "Default programs" in the Control panel or start menu. Choose "Associate a file type..etc. Scroll down to zip, near the bottom. It will normally have an associate. This may be IE, or perhaps you would like to select, top right "Change program". and select the "7" program from the choices.