Some may disagree but I find Firefox's default GTK "Save as" dialogue extremely annoying.
Compare
this to
this.
Here's how to get Firefox to display the second one.
1. In the address bar type
about:config. You will get some warning about breaking things, go right on through this.
2. In the filter bar, type in
ui.allow. You should now see the preference
ui.allow_platform_file_picker.
3. Double click on this to change it to
false.
4. Enjoy a much easier to use file save dialogue.