Hi idmswtg, where are you viewing your bookmarks? For example:

• Bookmarks Menu from the top menu bar (File, Edit View -- tap the Alt key to activate)
• Bookmarks Menu from the optional Bookmarks Menu toolbar button
• Bookmarks Sidebar that opens to the left of the current page
• Bookmarks Toolbar that appears below the main toolbar/address bar
• Somewhere else...

You can enlarge the font size of the toolbar area using a global zoom factor. Here are the details:

By default, Firefox follows your Windows "Text Size" setting. On laptops, that's often 125%. On desktop systems, it may be 100%. But Firefox also lets you override this and specify your own scaling factor.

This will scale up both the text and the icons in the toolbar area, and in web pages. Here's how to give it a try:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste devp and pause while the list is filtered

(3) Double-click the layout.css.devPixelsPerPx preference and enter 1.5 and click OK. This is equivalent to setting the "Text Size" in Windows to 150%.

What do you think, is this the same, better, too large? You can experiment with this setting, but I suggest not making it smaller than 1 and not making it larger than 3.

If things get out of control, you can right-click the setting and choose Reset, which is the bottom item on the right-click context menu.

Can you find a size that works well overall?

So that addresses the font size but doesn't address which font face is used or whether it is regular or bold. Those are a little trickier to change, particularly if you only want to change them in Firefox and not in your Windows settings (affecting multiple applications).