Apple Macintosh System 7.5 - Manual (Page 109)

4 Close the Extensions Manager to continue startup.
5 When the computer is ready, try the same actions that caused the problem.
If the problem does not occur again, then the item is probably compatible
with System 7.5.
If the problem occurs again, the program is probably incompatible. Open the
Extensions Manager and click the program’s name to remove the check.
6 Repeat steps 1 through 5 for each item you want to test.
101 Testing for Compatibility