http://wiki.greasespot.net/Talk:0.7.20080121.0_compatibility
Greasemonkey and Firefox 3 Beta Versions
This version of greasemonkey supports Firefox 3 Beta 4, but not Beta 5
(the most recent Beta as of April 4/08).
0.7.20080121 will run in Beta versions of Firefox using the following
workaround.
CAUTION:Using this workaround may crash your browser. ALL extensions
you have installed on Firefox will run if you use this workaround.
Enable extensions one at a time and restart Firefox 3. If Firefox 3
will not respond, use the method shown below to start the browser in
the Safe Mode.
For testing purposes you can tell the application to somewhat ignore
compatibility checks when installing add-ons. Simply create the
boolean
preference extensions.checkCompatibility and set it to false.
WARNING: this may crash your browser.
How to Start Firefox in the SAFE MODE to recover from incompatible
extensions.
Poorly designed or incompatible extensions can cause problems with
your browser, including make it crash, slow down page display, etc. If
you encounter strange problems relating to parts of the browser no
longer working, the browser not starting, windows with strange or
distorted appearance, degraded performance, etc, you may be suffering
from Extension or Theme trouble. Restart the browser in Safe Mode.
On Windows, start using the "Safe Mode" shortcut created in your Start
menu or by running firefox.exe -safe-mode.
On Linux, start with ./firefox -safe-mode.
On Mac OS X, run: cd /Applications/Firefox.app/Contents/MacOS/
./firefox-bin -safe-mode
When started in Safe Mode all extensions are disabled and the Default
theme is used. Disable the Extension/Theme that is causing trouble and
then start normally.