Here are a few possibilities that you can check:
There's a preference setting for windows: "Enlarge contents to improve readability". Any chance that option was previously selected and now isn't?
Have you changed your monitor's screen resolution?
"In find mode I can only enter one field"
Can only enter one field because only one is large enough to work with, or is it that you can't put the cursor in any of the other fields, or ...?
Fields can be set to deny access in find mode, check Field/control | behavior if this might be the case. Also, any fields with global storage and any fields that are <<merge fields>> can't be entered while in browse mode. (Merge fields can't be entered in any mode.)