Internet Explorer type issue in vista

MY Dell Inspiron 1525 running Internet Explorer 7.0 on Vista for 1 year.

When I type in my email (Hotmal, Gmail) and other text boxes, it is very slow and misses letters, though the issue is not with the keyboard itself.
Nothing seems to solve it.

1.Is your system fully updated Windows and Anti Virus First?
2.You can try it like:
Open Internet Explorer> Tools > Manage add-ons, disable all add-ons.
3.Does the third-party programs such as ad-blockers, appearance tweakers, etc cause the problem.
4.You can try another browser such as Firefox to see if the problem still exists.