If you have any add blocker addons make sure you have these sites added to your trusted sites list. Also try clearing all your browser cache (you can keep cookies to retain site specific logins).

Unfortunately I can't login to RenWeb to look at the actual drop-downs and run tests. If neither of the provided suggestions solve the problem, try to give me a link to a site with some drop-downs that are giving you problems. If I can identify the problem components I can find the likeliest cause.

Are you talking about the website menus, or Firefox?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies
  Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences<Enter> in the address bar.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

In some cases this happens because the JavaScript or CSS code that is used is not compatible with Firefox.

Can you post a link to a publicly accessible page (i.e. no authentication or signing on required)?