If this problem is for the Firefox pls set the browser to select the default font and color for the site you browse, if you have set your preferred font and color pls remove....this should solve the problem.
If this is system related issue , then check your system brightness/contrast setting for the desired clarity and brightness....in case you are not able to then their must be some harware issue that needs to be checked & requires repairs
Answers & Comments
If this problem is for the Firefox pls set the browser to select the default font and color for the site you browse, if you have set your preferred font and color pls remove....this should solve the problem.
If this is system related issue , then check your system brightness/contrast setting for the desired clarity and brightness....in case you are not able to then their must be some harware issue that needs to be checked & requires repairs
Warm Regards.