Did you explore the options for javascript and css in the system settings?
The latest versions of modx are constantly improving their speed, so make sure to update to the newest version regularly.
The choice of browser can also impact performance. I personally find Chrome to be the fastest, likely due to its superior javascript engine.
In addition, you can customize the manager to have separate administrative logins for each context or website by creating specific admin users with restricted access. The modx forums offer plenty of guidance on how to do this.
**EDIT***
There are various options in the manager that you can adjust to potentially improve performance:
- Enable Compressed CSS
- Enabling Compressed JavaScript Libraries
- Grouping When Compressing Javascript
- Setting Maximum JavaScript Files Compressed
- Adjusting Manager JS/CSS Compression Cache Age
Most of these settings should already be optimized by default.
There might be a way to disable the resource browser from refreshing every time you save, but I cannot recall the exact method at the moment.
If your administration access has been limited to specific contexts, you shouldn't be able to view resources outside of those contexts. If you still see other resources, it indicates some level of access beyond what is intended. It appears that your issue lies in the time it takes for the resource browser to refresh, rather than the server processing time, correct?