Hello Brothers,
I'm experimenting with this problem right now. I found a few surprises after changing operating systems and getting away from older software. I've never used screen resolutions above 800 x 600 before, but you have to if you want to use recent software. So, going to 1024 x 768 was a pretty big shock for me. It changes everything. Firefox is capable of making the fonts as big as you want them, but everything starts looking strange beyond a certain point.
I'm experimenting with "User Style Sheets", and this does work with several popular browsers, including Firefox, Opera, and a few others. "User Style Sheets" also effect everything else, but they do give you a lot of choices - all the way down to selecting fonts.
I'll give everyone a laugh about my changing screen resolutions. I really didn't want to change to the higher resolution, so I tried a few programs that weren't designed to work in a resolution as low as 800 x 600. I couldn't even see parts of the configuration menus, so I changed the resolution temporarily to 1024 x 768 to get the configurations done and changed back to what I really wanted - 800 x 600. Should I go ahead and tell you that many things disappear in those programs that are designed for 1024 x 768 and higher.

Needless to say, I have to use 1024 x 768 or not use the programs. Most of the programmers now view 800 x 600 as stone age stuff, and it's being phased out by nearly everyone. Old guys like me will just have to change, so I am trying to change. That doesn't mean that I have to like it.

I'm also experimenting with accessibility features that are available in most operating systems. They also effect everything. SO, most folks still have quite a bit of older software that works fine under 800 x 600 with good visibility because they were designed for that resolution or lower. You mix in the newer software that was designed for 1024 x 768 or higher, and you get some interesting problems. This is where "User Style Sheets" come to the rescue. Many programs will work with "User Style Sheets" and you can set individual programs for whatever you want, but they are a lot of work. If I remember correctly, they have sites for Firefox to help users do this quicker and with less work. You look at the effects of each change, decide if it's going to help or not, and either keep or discard the change. Many programs use "User Style Sheets" whether they tell you about them or not. Many of them do have a file extension of ".uss", so you can look in the program's main directories and find out. If you want to play with these, do yourself a favor and keep the old style sheets so you can go back to them if needed.
I'm curious, how many folks with problems seeing are still using the older 800 x 600 resolution? I ask this because 800 x 600 is larger everything, and there are fewer visibility problems in the lower resolutions.
Love In Christ,
Tom